GB1570979A - Polyesters - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO POLYESTERS (71) We, DYNAMIT NOBEL AKTIENGESELLSCHAFT, a German company of 521 Troisdorf, bez Kiln, Postfach 1209, Germany (Fed. Rep.), do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to polyesters and is particularly but not exclusively concerned with polyesters which contain halogen atoms to give them a flameproofing effect and which contain unsaturated components to improve their resistance to hydrolysis.

It is known to produce saturated linear polyesters by condensing an acid com- ponent with an alcohol component. Thus polyesters having acid components derived from aromatic and/or aliphatic and/or cycloaliphatic dicarboxylic acids or dicarboxylic acid mixtures, and alcohol components derived from dihydric alcohols are already known. The aromatic dicarboxylic acids which are preferably used in such polyesters are terephthalic acid and isophthalic acid or functional derivatives thereof, whilst preferred aliphatic dicarboxylic acids are primarily adipic acid, azelaic acid and sebacic acid. The cycloaliphatic dicarboxylic acids which are conventionally used are cyclobutane dicarboxylic acid, cyclopentane dicarboxylic acid, cyclohexane dicarboxylic acid and cyclohexylene diacetic acid. Conventionally preferred dihydric alcohols are ethylene glycol neopentyl glycol and 1,4-butane diol, and also mixtures thereof.

Technologically significant polyesters which are known are, for example, polyethylene terephthalate (PETP) and polytetramethylene terephthalate (PTMT).

One important property for certain applications of such polyesters is.their noninflammability. It is standard practice to make polyesters substantially non-inflammable or completely non-inflammable by adding fire-retarding substances to them during their production or processing. In general, organic or inorganic low molecular weight compounds containing halogen or even phosphorus and nitrogen, or mixtures of these compounds with metal oxides or non-metal oxides, which occasionally enhance one another's flameproofing effect, are used for this purpose. In addition to their desired flameproofing effect, additions such as these to polyesters always produce side effects which are generally undesirable because they adversely affect the characteristic properties of the polyesters and restrict their usefulness. Thus, all the flameproofing agents which are conventionally added to the polyester in powder form and which remain intact as powders in the matrix or, after melting and mixing during processing, separate out again on cooling as a separate phase, inevitably act not only in the required flameproofing manner, but also as fillers. As fillers, such agents alter the mechanical properties of the polyester; they generally have an embrittling effect and adversely affect elongation at break and impact strength.

In addition, conventional flameproofing additives which melt on incorporation into the polyester also generally give rise to disadvantages. In many cases, when considering the temperatures at which processing takes place, they have either vapour pressures which are too high or decomposition temperatures which are too low. In almost every case, the flameproofing agents added show a greater or lesser tendency to diffuse out of the plastics material again or to be dissolved out in cases where liquid processing media are used. As a result of this diffusion, not only are the noninflammable characteristics of the flameproofed polyesters gradually eliminated, but plastics thus flameproofed are also unusable for numerous applications, for example in the construction of electrical equipment.

Another conventional method of producing flameproof linear polyesters is to add chlorine-, bromine- or phosphorus-containing condensation components during the actual polycondensation stage, so as to form copolyesters with chlorine-, bromine or phosphorus-containing basic units. Thus in polyesters flameproofed in this way "flame proofing agent" is bound to the matrix by a homopolar bond and is therefore unable to chalk out; further, the flameproofing efficiency is optimised by virtue of the extremely homogeneous distribution of the flameproofing agent.

However, polyesters modified in this way generally show a modified property spectrum, in particular a different glass temperature and, in the case of crystallising products, modified crystallisation behaviour as well. In addition to reducing the melting temperature of the polyester, the use of flameproofing condensation components also usually reduces the degree of crystallisation, the crystallisation rate and also the seedforming rate (corresponding to fairly extensive super-cooling or to a delay in the beginning of crystallisation during cooling from the melt). The crystallisation behaviour of copolyesters such as these and more especially their inadequate tendency towards crystallisation can be of advantage in certain circumstances, though, for example for transparent mouldings to be produced by injection moulding or extrusion. Thus, pure PETP can only be used to a limited extent for the production of transparent mouldings on account of its tendency towards crystallisation. By contrast, copolyesters based on ethylene glycol as alcohol component, and, as acid component, a mixture of terephthalic acid dimethyl ester and a chlorine-containing dicarboxylic acid ester, namely bis (p-ethoxycarbonylphenoxymethyl)-2,3,5,6-tetrachlorobenzene, in a molar ratio of 1:0.2, are known to be amorphous and transparent (H. Haberlein and H. Kor- banka, Angew, Makrom. Chemie 33 (1973) 111).

It is also known to produce unsaturated polyesters in the form of resins (UP-resins) by techniques similar to those indicated above, with the difference that the acid component includes both unsaturated dicarboxylic adds and saturated dicarboxylic acids.

One important requirement for certain applications of UP-resins is their resistance to hydrolysis in acid or alkaline media, or their non-inflammability.

UP-resins which are classed as resistant to hydrolysis have already been described.

Thus it has been found that, by using as condensation components polyhydric alcohols which give rise to the formation of sterically hindered or masked ester groups, for example neopentyl glycol, it is possible to obtain UP-resins which are more resistant to hydrolysis than the UP-resins obtained in cases where ethylene glycol or butane diol is used. The use of isophthalic acid instead of other saturated dicarboxylic acids, such as terephthalic acid or orthophthalic acid, also makes it possible to synthesise UP-resins with improved resistance to hydrolysis by comparison with standard formulations based on ethylene glycol, phthalic anhydride and maleic anhydride. In addition, it is also known to be possible, by using fumaric acid as the unsaturated dicarboxylic acid or by using maleic acid (anhydride) with subsequent isomerisation of the maleic acid ester structures into fumaric acid ester structures, not only to improve the dimensional stability under heat, but also the resistance to hydrolysis of UP-resins hardened with styrene in relation to other standard UP-resin formulations.

Another method of obtaining UP-resins with greater resistance to hydrolysis is described in German Patent Specification No. 1,126,609 and in German Offenlegungs schrift No. 2,301,159. In this case, the diol components used are ethers of ethylene glycol or diethylene glycol with chlorinated biphenyl structures, for example bis (,ss-hydroxyethoxy)-octachlorobiphenyl corresponding ro the structural formula:

or bistetrachlorophenoxyethoxy ethanol corresponding to the structural formula:

Although the UP-resins obtainable from such diol components generally show increased resistance to hydrolysis by comparison with other standard UP-resins they only have moderate dimensional stability under heat.

According to one aspect of the present invention there is provided a polyester containing structural units of the formula

in which R1 represents an alkylene radical (as hereinafter defined) having from 2 to 10 carbon atoms, a cycloalkylene radical or a divalent radical derived from a hydroxyl group-terminated oligomeric alkylene terephthalate, and in which the divalent radicals R include (a) radicals having the general formula

or

wherein X independently represents hydrogen, bromine or chlorine and Z represents

and, optionally, (b) radicals which are unsaturated, with the proviso that in the case wherein R does not include unsaturated radicals at least one of the substituents X of general formula (15) represents bromine.

Another aspect of the invention provides a process for producing such polyesters which comprises condensing (i) a dicarboxylic acid component comprising (a) a saturated dicarboxylic acid of formula HOOCR COOH (12) or an ester forming derivative of such a saturated dicarboxylic acid, and optionally, (b) an unsaturated dicarboxylic acid or ester forming derivative thereof, and (ii) a dihydric alcohol component com prising a saturated alcohol of formula HO-R'-OH (13), to form the desired polyester.

In the case where the dicarboxylic acid component consists of saturated dicarboxylic acids or ester forming derivatives, then the polyester is, of course, a saturated linear polyester which, when containing structural units of formula (15), is necessarily brominated. However it is also possible for the acid component to include one or more unsaturated acids or ester forming derivatives, in which case the polyester is itself unsaturated and need not necessarily be brominated.

Where the polyester contains halogen atom substituents, for example where the substituents X of formula (14) or (15) are bromine and/or chlorine atoms, then, as discussed above, its flameproofing characteristics are generally improved.

In one embodiment of the invention, it is particularly preferred that the polyester consists entirely of structural units of formula (11) in which the divalent radical R has the formula (14) or (15), i.e. the dicarboxylic acid component consists entirely of the acid of formula (12) or an ester forming derivative thereof. Alternatively from 1 to 100 mol %, preferably from 2 to 10 mol %, of the structural units may have R of formula (14) or (1 5). In this case it is preferred that the balance of the structural units, i.e. up to 99 mol % and, for example, from 90 to 98 mol %, have R representing a phenylene radical and/or a naphthylene radical and/or an alkylene radical with 3 to 10 carbon atoms and/or a cycloalkylene radical.

With regard to the general formulae (14) and (15) represented by R, it is preferred that the terminal phenylene groups are para-substituted, although they may alternatively be ortho- or meta-substituted. The central nucleus of formula (15) may be ortho, meta- or para-substituted.

In the case where the divalent radicals R are halogenated, each X of formula (14) or each X of the central nucleus of formula (15) may represent a bromine atom, or alternatively a chlorine atom. As yet another alternative, these four substituents X may include both bromine and chlorine atoms. For example the four substituents X of the central nucleus of formula (15) may include on average from 4.0 to 2.8 preferably from 4.0 to 3.0 bromine atoms, and from 0 to 1.2, preferably from 0 to 1.0 chlorine atoms.

The divalent radicals R included in the structural units of polyesters according to the invention may be derived from acids and esters having the general formula

in which X and Z are as defined above with reference to general formulae (14) and (15), and each R" independently represents hydrogen or an alkyl radical having up to 6 carbon atoms. Certain of these compounds form the subject of our copending British Patent Application 7,913,804 (Serial No. 1,570,980) which is divided out of this application.

In these compounds the terminal phenylene groups are, again, preferably para substituted, and R" preferably represents an alkyl radical having up to 4 carbon atoms such as methyl, ethyl, n-propyl or i-propyl, with the dimethyl esters being the preferred compounds. When the compounds are halogenated, in addition to the pure bromine or chlorine substitution products in structural formulae (4) or (5), other useful bisesters and acids have been found to be those in which part of the bromine is replaced by chlorine, generally by no more than one chlorine atom per molecule (4.0 > Br) 3.0; 1 Cl > 0).

The small chlorine content may emanate from a bromine-chlorine exchange during production of the compounds or during the production of the tetrabromoxylylene dichloride which may be used in their production and which is itself obtainable by the side-chain chlorination of tetrabromoxylene. In cases where the nuclear halogen has been introduced by bromochlorination during production of the intermediate compound, the chlorine content may even arise from the use of bromine which contains chlorine.

It is preferred that the dicarboxylic acid component additionally comprises terephthalic acid, isophthalic add, naphthalene dicarboxylic acid, adipic acid, azeleic acid, sebacic acid, cyclobutane dicarboxylic acid, cyclopentane dicarboxylic acid, cyclohexane dicarboxylic acid, cyclohexylene diacetic acid or ester forming derivatives thereof or mixtures thereof. Alternatively or as well, the dicarboxylic acid component may additionally comprise orthophthalic acid, tetrahydrophthalic acid, endomethylene tetrahydrophthalic acid or hexachloroendomethylene tetrahydrophthalic acid or ester forming derivatives thereof or mixtures thereof.

The alkylene radicals R' of the polyester structural units of formula (11) and of the dihydric alcohols of formula (13) are defined as follows: they may be optionally branched simple alkylene radicals; alternatively they may include an oxygen atom or an arylene group in the carbon chain. Thus the alkylene radicals R' may be based on, for example neopentyl glycol, ethylene glycol, 1,2-propane diol, 1,3-propane diol, 1,3butane diol, 1,4-butane diol, 1,2-butane diol, diethylene glycol, 1,6-hexane diol, 1,4or 1,3-bis-(hydroxymethyl)-cyclohexane, meta- or para- xylylene glycol, or meta- or para- tetrabromo or tetrachioro xylylene glycol, or mixtures thereof.

The diol component of the polyesters may be based on hydroxyl group-terminated oligomeric alkylene terephthalates, preferably those having a reduced specific viscosity of from 0.05 to 0.5, more preferably from 0.1 to 0.2. For example the alkylene radical of the oligomer may be ethylene, propylene or butylene, preferably straight chain butylene ie tetramethylene. Thus suitable diol components are, for example, oligomeric pre-condensates, containing terminal hydroxyl groups, of terephthalic acid, preferably its dimethyl ester, with alkylene glycols of formula (13). They may be used as sole diol components or together with one or more other diols, preferably 1,4-butane diol and/or ethylene glycol. Preferred oligomeric precondensates are derived from terephthalic acid, preferably from its dimethyl ester, and ethylene glycol and/or 1,4-butane diol.

As mentioned above, the polyester according to the invention may be unsaturated, i.e. the divalent radicals R may include radicals which are unsaturated, such as ethenylene radicals. Accordingly, in the production of such unsaturated polyesters, the dicarboxylic acid component additionally includes an unsaturated dicarboxylic acid or ester forming derivative thereof, for example maleic acid, maleic anhydride or fumaric add. Thus in these polyesters the saturated dicarboxylic acid components are partly replaced by unsaturated dicarboxylic acid derivatives. These, together with ethylenically unsaturated comonomers, preferably styrene, are able to form peroxidically posthardenable unsaturated polyester resin (UP-resin) solutions.

It is preferred that the unsaturated polyesters contain, as their saturated acid component, from 2 to 100 mol% and more preferably from 5 to 80 mol% of radicals having the formula (14) or (15), based on the total amount of saturated radicals R.

The UP-resins are preferably used as cast resins for the production of mouldings in the form of their solutions in a monomer which is copolymerisable with, for example, the maleate or fumarate double bonds, preferably styrene. Following the addition of radical formers, the UP-resin solution, optionally containing fillers or reinforcing materials, is hardened after moulding and optionally post-hardened. Suitable radical formers are, for example, peroxides, preferably dibenzoyl peroxide, used either on their own, for example in the form of a 50% paste, or together with tertiary amines as accelerators.

In the process according to the invention, the acid component and the diol component are preferably condensed in a molar ratio of from 1:1.1 to 1.5, and more preferably in a molar ratio of from 1:1.2 to 1:1.4. The condensation is preferably carried out by first transesterifying the acid and alcohol components in the presence of a transesterification catalyst, and then polycondensing the transesterification product in the presence of a polycondensation catalyst. Suitable transesterification and polycondensation catalysts for the production of the polyester resins according to the invention are the compounds commonly used for transesterification and polycondensation reactions, for example zinc acetate, manganese acetate, germanium dioxide or titanium esters. It is preferred to use the titanium esters, for example tetrabutyl titanate or the transesterification product of tetrabutyl titanate and 2-ethyl-1-, 3-hexane diol. The catalysts are preferably used in quantities of from 0.01 to 0.2% by weight, and more preferably in quantities of from 0.015 to 0.5% by weight, based on the sum of the polycondensation components.

On account of the sensitivity of the reactants, especially the alcohol components, to oxidation at the high condensation temperatures applied, both the transesterification stage and also the polycondensation stage are generally carried out in an inert gas atmosphere or in vacuo. Esterification or transesterification is preferably carried out at a temperature of from 150 to 220 C, and more preferably from 160 to 2000 C. The subsequent polycondensation stage is preferably carried out at a temperature of from 200 to 2500 C and substantially in vacuo, preferably at a reduced pressure falling continuously or in stages to 6 1 Torr.

In general, then, the dicarboxylic acid esters or dicarboxylic acids of structural formulae (4) or (5) are transesterified or esterified either individually or in admixture with non-brominated dicarboxylic acids or dicarboxylic acid esters with the diols or diol mixtures used, in the presence of transesterification or esterification catalysts and subsequently polycondensed by increasing temperature, preferably in vacuo, during transesterification or esterification and removing the excess or eliminated alcohols and water from the equilibrium until the product of required molecular weight is obtained.

The oligomeric alkylene terephthalates which may be employed as alcohol component may be produced for example, in the same way as described in German Offenlegungsschriften 2,504,156 and 2,504,258.

By way of example, a general embodiment of the process of the invention will now be described. Dimethyl terephthalate and a diol in a preferred molar ratio of from 1:1.1 to 1:1.5 and more preferably in a molar ratio of from 1:1.2 to 1:1.4, and a catalyst, are continuously introduced into the uppermost chamber of a heatable reactor consisting of several interconnected chambers arranged vertically one above the other. A transesterification reaction is carried out under normal pressure at temperatures which increase from the base of one chamber to the base of the next chamber until the required degree of condensation, preferably corresponding to a reduced specific viscosity of from 0.05 to 0.5, more preferably from 0.1 to 0.2, is reached, with excess diol being subsequently removed. In order to complete the reaction, condensation is then carried out in further directly connected or separated chambers at an increased temperature and in a corresponding vacuum. In general, the temperature at the beginning of the transesterification reaction in the uppermost chamber is from 130 to 1600 C and rises to between 180 and 210 C in the lowermost chamber of the normal pressure stage. The condensauion of the transesterification product generally takes place in vacuo at a temperature in the range from 180 to 2500 C and preferably at a temperature in the range from 220 to 2400 C. The pressure is generally in the range from 300 to 20 Torr and preferably in the range from 250 to 50 Torr.

The ester compounds of structural formulae (4) and/or (5) are preferably used for the production of modified polyethylene terephthalates or polytetramethylene terephthalates because production of the corresponding free acids involves another process step. Thus the condensation components of structural formula (4) and/or (5) may be directly added to the oligomeric precondensates of DMT with ethylene glycol (OET) or of DMT with 1,4-butane diol (OBT) and polycondensed in admixture until the required molecular weight is obtained. However, it is also possible initially to esterify the condensation components of structural formula (4) or (5) with ethylene glycol or 1,4-butane diol when they are in the form of their free acids, or to transesterify them in the case of the ester derivatives, and then to add the oligomeric precondensates OET or OBT, followed by polycondensation.

By varying the molar ratios of the dicarboxylic acid mixtures or by combining the bis-esters or dicarboxylic acids of structural formulae (4) and/or (5), which may also be used in accordance with the invention as sole dicarboxylic acid component, with a diol or diol mixture, it is possible to adapt halogen-containing saturated linear polyester resins to the required application in regard, for example, to their mechanical or optical or flameproofing properties.

Halogen-containing polyester resins according to the invention which have been found to have interesting properties are, for example, those in which from 2 to 10 mole % of the radicals R correspond to the general formulae (14) and/or (15) and 90 to 98 mole % to the terephthalic acid radical, the radical R' being an ethylene radical and/or a tetramethylene radical.

Other halogen-containing polyesters with interesting properties are those in which 100% of the radicals R correspond to general formulae (14) and/or (15) whilst the radical R' is derived from an oligomeric alkylene terephthalate, preferably from an oligomeric ethylene or an oligomeric tetramethylene terephthalate.

In general, the reduced specific viscosities of the saturated polyesters according to the invention are from 0.5 to 2.5 and preferably in the range from 0.8 to 1.6, as measured in 1% phenol/o-dichlorobenzene solution (ratio by weight 60:40) at 25 C.

The halogen content of the saturated polyesters according to the invention are preferably from 1 to 30% by weight and more preferably from 3 to 10% by weight.

It is known that for PETP as a plastics material, it would be of advantage to have either a relatively high crystallisation rate or a very low crystallisation rate (absence of any relatively pronounced crystallisation). For PTMT, a fairly heavily reduced crystallisation rate would be a disadvantage for most applications. It has been found that linear copolyesters based on PETP or PTMT and which contain structural units of formula (11) according to the invention have certain unexpected properties. Thus PETP modified in this way is greatly disturbed or inhibited in its crystallisability, whereas the crystallisability of similarly modified PTMT is the same as or even greater than that of unmodified PTMT.

It has been found in some specific embodiments that the use of bis-esters corresponding to structural formulae (4) and/or (5) in addition, for example, to dimethyl terephthalate in quantities of only 5 mole%, based on the total quantity of dicarboxylic acid component, enables a PETP which is amorphous even after tempering to be produced. Further, modified polytetramethylene terephthalates including radicals of the structural formulae (14) and/or (15) used in quantities of up to 10 mole %, based on the total quantity of dicarboxylic acid radicals, show an even more favourable crystallisation behaviour than PTMT: the melting temperatures are only negligibly reduced, i.e. by a few degrees, in relation to pure PTMT, whilst the crystallisation rate and degree of crystallisation are, surprisingly, even increased to a slight extent In addition, relatively gentle supercooling of the copolyesters on cooling from the melt produces an increased seed-forming rate. Another advantage of such linear polyesters according to the invention, is their increased resistance to hydrolysis in acids and alkalis. The reduction in molecular weight on contact with these agents is greatly reduced in relation to unmodified polyesters. Further, the presence of structural units having halogen substituents has the effect of flameproofing the polyesters.

Polyesters according to the invention have been found generally to have an increased glass temperature compared with polyesters not containing structural units of formula (11). For example, the glass temperature of a weakly crystalline PETP is increased from 63 C (as determined by differential thermoanalysis) to 82" C by the incorporation of 7 mol % of the units of structural formula (11) where R is of formula (15), based on the total of acid basic units.

Although experience has shown that the use of bromine-containing reaction components either alone or in combination with other non-brominated components in melt condensation processes taking place at temperatures in the range from 2200 C to 2800 C leads to brown or reddish-brown discolourations of the polycondensates, modified polytetramethylene terephthalates according to the invention, i.e. PTMT modified by the inclusion of structural units of formula (11), are substantially unchanged in regard to colour by comparison with pure PTMT. This is surprising because the polyesters PTMT and PETP modified with the chlorine-substituted, as opposed to bromine-substituted, structural units of formula (11) show intensive yellow or brownish-yellow discolouration and, in general, a considerably higher resistance to discolouration under heat is attributed to organic aromatic chlorine compounds than to the corresponding bromine compounds.

In cases where the halogen-containing polyesters of the invention are used as polymer component in moulding compositions optionally containing fillers such as reinforcing fillers, and, optionally, standard additives, such as pigmenting agents and/or mould release agents, it has been found that flameproofed or fire-retarding moulding compositions are obtained. It is preferred to add synergistically acting fire retarding agents such as antimony or boron compounds, preferably antimony trioxide, to moulding compositions of this type. The quantities added are preferably in the range from 2 to 12% by weight and more preferably in the range from 4 to 7% by weight, based on the composition as a whole.

Reinforcing fillers which may be incorporated are, for example, glass powder, glass beads or glass fibres. Preferred reinforcing fillers are glass fibres which may optionally be sized in known manner. In general, the reinforcing filler is preferably used in quantities of from 2 to 60% by weight, based on the composition as a whole.

The additives, such as reinforcing fillers, may be incorporated in known manner, preferably by compounding in the melt. Moulding compositions according to the invention may be processed by conventional moulding techniques, such as extrusion or injection moulding, to form shaped structures.

When the polyesters of the invention contain unsaturated structural units, i.e. are UP-resins, they have generally been found to show considerably improved resistance to hydrolysis by comparison with known UP-resins conventionally classed as resistant to hydrolysis. Another unexpected advantage is the increased dimensional stability under heat of mouldings obtained from them by hardening with styrene. Typically, the dimensional stability under hea 1200 C and hence is higher by 10 to 30 degrees C than that of standard commeråal- grade UP-resins of which the dimensional stability under heat according to Martens is about 900 C.

Another property of the halogenated UP-resins according to the invention and to mouldings produced therefrom is their resistance to fire; certain resin formulations have been found to reach the UL classification VO in UL test No. 94 without additives such as phosphorus or Sb2O,, whilst other resin formulations according to the invention can be made self-extinguishing by the addition of small amounts of synergistically active substances.

Accordingly, the invention also relates to the use of the unsaturated polyesters according to the invention as components of compositions which are solutions of the polyesters in copolymerisable monomers, which compositions are used for the production of mouldings which are resistant to hydrolysis and dimensionally stable under heat and, in cases where the bromine and/or chlorine containing UP-resins according to the invention are used, optionally together with synergistically active additives, for the production of flameproofed, self-extinguishing mouldings. Mouldings of this type preferably contain from 5 to 25% by weight and more especially from 8 to 18% by weight of organically bound bromine and from 10 to 30% by weight of organically bound chlorine.

In the production of UP-resins according to the invention the unsaturated dicarb oxylic acid component is preferably used in quantities of from 30 to 80 mole % and more preferably from 40 to 70 mole %, based on the total quantity of dicarb oxylic acid component used. The polyhydric alcohols used may be the diols known per se for the production of UP -resins, for example ethylene glycol, diethylene glycol, 1,2-propane diol, 1,4-butane diol, cyclohexane dimethanol, meta- or para-sylylene glycol, tetrachloro-m or p-xylylene glycol or neopentyl glycol. Although it is pre ferred to use neopentyl glycol for the production of UP-resins with a high resistance to hydrolysis, it has be.en found to be an advantage of using the ester compounds of structural formula (4) and/or (5) as saturated components in the polymer linkage that substantially hydrolysiresistant resin formulations can also be produced from or with ethylene glycol (and also from or with orthophthalic acid, i.e. starting from sub - stantially standard formulations).

The saturated dicarboxylic acid component of the unsaturated polyesters may be the esters of structural formulae (4) and/or (5) either alone or together with the dicarboxylic acids which are conventionally used in the production of UP-resins, optionally in the form of their anhydrides or other polyester-fowTning derivatives. For example there may additionally be used adipic acid, orthophthalic acid or its anhydride, tetrahydrophthalic acid, endomethylene tetrahydrophthalic acid, tetrachlorophthalic acid, hexachloroendomethylene tetrahydrophthalic acid, isophthalic acid, terephthalic acid or dialkyl esters thereof or mixtures of the individual components. In addition to the esters of structural formulae (4) and/or (5) it is preferred to use isophthalic acid and/or terephthalic acid. Terephthalic acid is generally used in the form of its dimethyl ester. Although isophthalic acid is known as a component of hydrolysis-resis tant UP-resins, comparison tests have shown that resistance to hydrolysis can be considerably improved by partly or completely replacing the isophthalic acid by the esters of structural formulae (4) and/or (5).

In the production of the UP-resins, the diols and the total (saturated and un saturated) dicarboxylic acid component are preferably used in a molar ratio of 1:1.

However the dicarboxylic acid component may optionally be present in a slight excess.

Whereas in general it has been found that the co-condensation of isophthalic acid, with otherwise the same resin formulation, gives UP-resins with distinctly better resistance to hydrolysis than those obtained with terephthalic acid, resin formulations which, in addition to the esters of structural formula (4) or (5) contain the same quantity of terephthalic acid instead of isophthalic acid in co-condensed form, have been found to be almost as good in their resistance to hydrolysis in the present case. For example, the UP-resin formulations: (a) 1 mole of neopentyl glycol, 0.2 mole of tetrachloro-m xylylene-bis-(4-methoxy carbonyl phenyl)-ether, 0.2 mole of terephthalic acid dimethyl ester and 0.6 mole of fumaric acid, or (b) 1 mole of neopentyl glycol, 0.2 mole of tetrachloro-m-xylylene-bis-(4-methoxy carbonyl phenyl)-ether, 0.2 mole of isophthalic acid and 0.6 mole of fumaric acid, dissolved as 60 parts by weight in 40 parts by weight of styrene and hardened show the same resistance to aqueous alkali or aqueous mineral acid.

It is known that chlorinated or brominated dicarboxylic acids or diols, for example tetrachlorophthalic acid, hexachloroendomethylene tetrahydrophthalic acid, tetrabromo phthalic acid or dibromobutene diol and dibromoneopentyl glycol, can be used as con densation components for the production of substantially non-flammable or selfextinguishing UP-resins and UP-resin mouldings. To reduced flammability in the polymer product, these compounds have to be co-condensed in quantities which allow the chlorine or bromine content of the end product (a UP-resin solution in styrene or a hardened moulding) to rise to beyond 20% by weight or 10% by weight, if the required flameproofing effect is to be obtained in the absence of synergistically acting flame retarding agents such as Sb2O, (which give rise to opacity in the mouldings which is undesirable for certain applications). Thus in cases where it is intended to produce selfextinguishing mouldings under the above-mentioned conditions, their chlorine content must be of the order of 30 /O by weight or their bromine content of the order of 17%.

However in order to introduce halogen contents as high as these into the UP-resins through the incorporation of the above-mentioned dicarboxylic acids, the dicarboxylic acids have to be used in such quantities that embrittlement, i.e. deterioration in impact behaviour and elasticity, of the product is inevitable.

In cases where the bromine content is introduced into the polymer through the above-mentioned bromine-containing diols, disadvantages can be expected on account of the comparatively poor stability of the aliphatic carbon-bromine bond. UP-resins produced in this way show a tendency towards brownish-red discoloration, even during their production, and towards spontaneous cross-linking at the polycondensation stage.

By contrast, it has been found that the unsaturated polyesters of the invention, produced for example by using the bromine-substituted esters of structural formulae (4) and/or (5) and, in particular, the tetrabromine-substituted esters, can have the halogen contents required for producing self-extinguishing properties in the UP-resins, resin solutions or hardened- mouldings without any undesirable discoloration or even crosslinking of the mixtures. Surprisingly, there has been found no evidence of any embrittlement; instead the dimensional stability under heat of the UP-resins or of the mouldings obtainable therefrom, which increases with the proportion of the structural units of formula (11) in the polyester, is actually accompanied by a slight increase in the impact strength of the mouldings.

As is the case with the saturated polyesters according to the invention, the UPresins are preferably produced by melt polycondensation, although the described polyesters can also be produced by polycondensation in solution or by azeotropic polycondensation. By way of example, a general embodiment of the production of unsaturated polyesters in accordance with the invention will now be described.

The dicarboxylic acid esters of structural formulae (4) or (5) are preferably first transesterified with the diols used and are only polycondensed with the remaining acid components on completion of transesterification. In cases where, in addition to the dicarboxylic acid esters of formula (4) or (5), other saturated dicarboxylic acids are used in the form of their dialkyl esters, for example terephthalic acid dimethyl ester, the latter may be transesterified together with the esters of formula (4) or (5). Transesterification may be carried out in known manner, preferably at temperatures of from 140 C to 2100 C and more preferably at temperatures of from 1500 C to 2000 C, in the presence of transesterification catalysts such as PbO2, zinc acetate, manganese acetate or titanium esters. Tetraalkyl titanates are preferably used for transesterification.

On completion of transesterification and after the remaining dicarboxylic acid components, especially maleic acid, preferably maleic acid anhydride, and/or fumaric acid, have been added, polycondensation is continued until the required molecular weight is obtained, by increasing the temperature in stages to at most 2400 C and preferably to between 200 and 2200 C. In cases where saturated free dicarboxylic acids, for example isophthalic acid, are also used as reaction components, it has been found to be preferable initially to add and co-condense the saturated dicarboxylic acids on completion of transesterification and to introduce the unsaturated dicarboxylic acids as the last reaction component. This sequence affords advantages especially in cases where isophthalic acid and fumaric acid are used. The UP-resins obtained generally contain smaller styrene-insoluble fractions, and the thermally more sensitive unsaturated dicarboxylic acids are not exposed for too long to the high condensation temperatures.

In order to accelerate the polycondensation reaction it is preferred to add esterification catalysts in quantities of from 0.02 to 0.2% by weight, based on the resin mixture as a whole. Examples of esterification catalysts which may be used are tetraalkyl titanates, tetraalkyl zirconates, dialkyl tin oxide and reaction products thereof with aliphatic carboxylic acids (Harada complexes). It is preferred to use the titanate of 2-ethyl-1,3-hexane diol, the zirconate of 2-ethyl-1,3-hexane diol, or sodium or potassium tetraphenyl borate.

On account of the sensitivity of the reactants, especially the alcoholic components, to oxidation at the high condensation temperatures, both the transesterification stage and also the polycondensation stage are carried out in an inert gas atmosphere.

The UP-resins of the invention preferably have molecular weights of from 1000 to 6000 and more preferably of from 2500 to 4000. Their reduced specific viscosities (1 g/100 ml in phenol/tetrachlorethane 60/40 at 250 C) are preferably from 13 ml/g to 26 ml/g.

The UP-resins may be used as cast resins for the production of mouldings in the form of their solutions in a monomer which is copolymerisable with the maleate or fumarate double bonds, preferably styrene. To form the castings, following the addition of radical formers, the UP-resin solution, (preferably containing from 20 to 80% by weight and more preferably from 40 to 70% by weight of UP-resin, with the balance being a copolymerisable monomer) and optionally containing fillers or rein forcing materials and, optionally, other conventional additives, the resin is hardened after moulding. It may then optionally be post-hardened, preferably at elevated temperatures, for example at temperatures of from 50 to 1500 C and more especially at temperatures of from 120 to 1400 C. The radical formers which may be used are, for example, peroxides, preferably dibenzoyl peroxide, either on their own, for example in the form of a 50% paste, or together with tertiary amines as accelerators. The hardened mouldings thus produced are generally colourless and, in most cases transparent.

UP-resins of the invention were tested for resistance to hydrolysis by storing the styrene-hardened mouldings for 30 days in 20% aqueous sodium hydroxide solution or in 25% aqueous sulphuric acid at a temperature of 850 C. The mouldings were examined, as specified in the following Examples, not only for external changes, such as crack formation or surface roughening, but also for any decrease in their flexural strength and for changes in weight.

The invention is illustrated by the following Examples. The values quoted both in the Examples and also in the Comparison Examples were determined in accordance with the following specifications: Flexural strength: DIN 53 452 Impact strength: DIN 53 453 Notched impact strength: DIN 53 453 Ball indentation hardness: DIN 53 456 Martens temp: DIN 53 458 ISO/R 75; A: DIN 53 461 Flammability: Underwriters' Laboratory (UL)-test EXAMPLE 1.

Tetrachloro-m-xylylene-bis-(4-methoxy carbonyl phenyl) -ether (general formula (5)) as acid component.

104 g (1 mole) of neopentyl glycol and 54.4 g (0.1 mole) of tetrachloro-m- ylylene-bis-(4-methoxy carbonyl phenyl)-ether, together with 0.1 g of the titanate of 2-ethyl-1,3,hexane diol as transesterification catalyst, were mtroduced into a reaction flask equipped with a stirrer and gas-inlet tube. Transesterification was carried out at a bath temperature increasing from 170 to 200 C. After the evolution of methanol had stopped, indicating that transesterification was over, 49.8 g (0.3 mole) of iso phthalic acid were added, followed by condensation for 30 minutes at 2000 C. 69.6 g (0.6 mole) of fumaric acid and 0.08 g of 2,4-di-tert.-butyl cresol were then added to prevent crosslinking during the polycondensation reaction, followed by esterifica tion for 30 minutes at 200 C. After the addition of 0.1 g of the zirconate of 2-ethyl 1,3-hexane diol as esterification caralyst, the mixture was polycondensed for 1 hour at 200 C and then for 3 hours at 220 C.

A substantially colourless unsaturated polyester resin, hereinafter termed UP-resin, was obtained with a molecular weight of 2900, as determined by gel chromatography in tetrahydrofuran (THF).

60 parts by weight of the UP-resin were dissolved in 40 parts by weight of styrene and the resulting solution was hardened in a mould using 2% by weight of dibenzoyl peroxide paste (50%) and 0.03% by volume of dimethyl aniline (in the form of a 10% solution in styrene). 4 mm thick panels were thus formed and were then post-hardened for 4 hours at 135 C.

The hardened resin panels had the following properties: Flexural strength: 105.6 N/mm2 Impact strength: 6.6 KJ/m2 Dimensional stability under heat: according to Martens: 1080 C according to ISO/R 75; A: 1230 C Respective panels were stored for 30 days in 20% aqueous sodium hydroxide solution, in 25% sulphuric acid at a temperature of 850 C and in chlorobenzene at a temperature of 400 C.

After storage, the test specimens showed no external changes; neither was there any sign of roughening or cracks in their surface. The specific storage results were as follows: (a) Storage in NaOH: The change in weight amounted to +0.16%1) and 0.23%2).

Flexural strength fell from 105.6 to 66.6 N/mm2, i.e. by 36.8%.

(b) Storage in H2SO4: The change in weight amounted to +0.17%1' and +0.09%2).

Flexural strength fell to 83.9 N/mm2, i.e. by 20.5%.

(c) Storage in chlorobenzene: The change in weight amounted to +2.5%1' and + 1.5%2'.

Flexural strength fell to 83.9 N/mm2, i.e. by 20.5%.

The weight change measurements were carried out as follows: 1) The test specimens were rinsed with distilled water and then with acetone and dried in air for 30 minutes (in the case of storage in chlorobenzene, the test specimens were only rinsed with acetone).

2) The test specimens were treated as in 1) above, but were dried in air for 3 days, as opposed to 30 minutes.

EXAMPLES 2 to 15.

Under the same reaction conditions as in Example 1, UP-resins were produced using different quantities of various bis-esters corresponding to general formula (5).

The bis-esters used were tetrachloro-m-xylylene-bis-(4-methoxy carbonyl phenyl)ether, tetrachloro-p-xylylene-bis-(4-methoxy carbonyl phenyl)-ether and p-xylylene-bis (methoxy carbonyl phenyl)-ether.

The UP-resins produced were dissolved in styrene and hardened in the same way as in Example 1. Similarly the resistance to hydrolysis of the panel mouldings produced was determined as in Example 1.

The resin formulations, the mechanical properties of the hardened mouldings, the changes in weight occurring during storage in sodium hydroxide and the decrease in flexural strength are shown in Tables 1 and 2.

Comparison Examples 1 to 5.

Following the procedure of Example 1, some resin formulations conventionally classed as resistant to hydrolysis were produced in the absence of the bistesters of general formula (5). The UP resins produced were subsequently hardened in the form of solutions in styrene and tested for their resistance to hydrolysis in the same way as in Examples 1 to 15.

The resin formulations and results obtained are set out in Table 3.

Comparison Example 6, details of which are also included in Table 3, relates to a standard UP-resin. The resistance to hydrolysis of panel mouldings produced from the resin was so poor that it was completely destroyed before the end of 14 days' storage in NaOH.

Although, as shown by Comparison Example 5, a slight improvement in resistance to hydrolysis was obtained by partly replacing the ethylene glycol with neopentyl glycol, and all the maleic acid with fumaric acid, the panel moulding was also completely destroyed after 30 days' storage in NaOH.

By replacing 0.1 mole of the phthalic acid with 0.1 mole of p-xylylene-bis-(4methoxy carbonyl phenyl)-ether in otherwise the same resin formulation as Comparison Example 5, resistance to hydrolysis could be considerably increased. Under the same hydrolysis conditions, the decrease in flexural strength amounted to just 47% (Example 15).

TABLE 1 Examples 2 3 4 5 6 7 8 Resin formulation: Neopentyl glycol [moles] 1 1 1 1 1 1 1 Tetrachloro-m-xylylene- " 0.05 0.15 0.2 0.25 0.3 0.3 bis-(4-methoxycarbonylphenyl)-ether Tetrachloro-p xylylene- " - - - - - - 0.2 bis-(4-methoxycarbonylphenyl)-ether Isophthalic acid " 0.35 0.3 0.2 0.2 0.15 0.1 0.2 Fumaric acid " 0.6 0.55 0.6 0.55 0.55 0.3 0.6 Maleic acid " - - - - - 0.3 Hardened mouldings: 8) Flexural strength [N/mm] 96.9 106.6 114.3 117.2 119.0 116.0 103.7 Impact strength [KJ/m] 6.9 7.2 7.4 8.2 8.6 9.2 5.9 Martens temp. [ C] 94 109 112 113 119 107 117 After storage in NaOH9) Flexural strength [N/mm] 46.6 86.4 102.0 105.5 110.2 90.7 92.1 Decrease in flexural strength [%] 51 19.5 11 10 7 27.8 11.2 Weight difference 1) [%] +0.37 +0.07 +0.12 +0.10 +0.09 +0.05 -0.04 2) [%] -0.18 +0.04 +0.08 -0.08 -0.01 -0.007 -0.26 -0.15 Remarks 4) 3) 3) 3) 3) 4) 3) After storage in chlorobenzene: Flexural strength [N/mm] 91.1 103.1 Decrease in flexural strength [%] 6 10 Weight loss 1) [%] +3.5 +3.4 2) [%] +2.6 +2.8 TABLE 2 Examples 9 10 11 12 13 14 15 Resin formulation: Neopentyl glycol [moles] 1 1 1 0.8 1 1 0.5 Ethylene glycol " - - - 0.2 - - 0.5 p-xylylene-bis-(4- " - - - - 0.15 0.3 0.1 methoxycarbonylphenylether Tetrachloro-m-xylylene- " 0.2 0.18 0.1 0.1 - - bis-(4-methoxycarbonylphenyl)-ether Orthophthalic acid " - - - - - - 0.3 Isophthalic acid " - 0.14 0.1 0.05 0.05 0.15 Terephthalic acid " 0.2 0.18 0.25 0.25 0.25 - Fumaric acid " 0.6 0.5 0.55 0.6 0.55 0.55 0.6 Hardened moulding: 8) Flexural strength [N/mm] 109 111 103 100.7 101.5 118 96.4 Impact strength [KJ/m] 6.8 8.9 7.7 6.5 8.2 9.1 6.2 Martens temp. [ C] 118 113 106 109 107 115 78 After storage in NaOH: 9) Flexural strength [N/mm] 98.3 96.0 91.5 82.0 93.6 109.8 52.1 Decrease in flexural strength [%] 10 13.5 11 18 7.7 7 47 weight difference 1) [%] +0.4 +0.38 +0.19 +0.7 +0.15 +0.2 -0.7 2) [%] -0.04 +0.09 -0.02 +0.17 -0.01 +0.06 -1.2 Remarks: 3) 3) 3) 4) 3) 3) 4) TABLE 3 Comparison Examples 1 2 3 4 5 6 Resin formulation: Neopentyl glycol [moles] 0.8 1 1 - 0.5 Ethylene glycol " - - - - 0.5 1 Bis-tetrachlorophenoxyethoxy ethanol " 0.2 - - - - Bisphenol A-bis-(B-hydroxyethyl ether " - - - 1 - Orthophthalic acid " - - - - 0.4 0.4 Isophthalic acid " 0.04 0.45 0.1 0.1 - Terephthalic acid " 0.36 - 0.35 - - Fumaric acid " 0.6 0.55 0.55 0.9 0.6 Maleic acid " - - - - - 0.6 Hardened moulding: 8) Flexural strength [N/mm] 99.9 119.7 107 98 84.0 76.0 Impact strength [KJ/m] 6.2 7.6 6.4 6.0 7.8 7.0 Martens temp. [ C] 89 91 93 92 64 55.0 After storage in NaOH: 9) Flexural strength [N/mm] 73.2 62.0 52.5 36.1 0 0 Decrease in flexural strength [%] 26 48 51 63 100 100 Weight difference 1) [%] +0.04 -0.9 -0.7 +3.2 - 2) [%0] -0.3 -1.3 -1.2 +1.9 - Remarks: 4) 5) 5) 5) 7) 7) Footnotes to Tables 1, 2 and 3: 1) See remarks after Example 1 2) 3) =no change in the moulding, completely smooth surface 4) =surface slightly roughened, but no cracks 5) =surface slightly roughened and cracks 6) moulding seriously affected 7) =moulding completely destroyed 8) =60 parts by weight of resin+40 pats by weight of styrene; hardening as in Example 1 9) 30 days in 20% aqueous sodium hydroxide at 850 C EXAMPLE 16.

Tetrabeomobisphenol A-bis-(4-methoxycarbonyl benzyl)-ether (structural formula (4)) as acid component.

72.8 g (0.7 mole) of neopentyl glycol, 13.8 g (0.05 mole) of tetrachloro-mxylylene glycol, 15.5 g (0.25 mole) of ethylene glycol and 302.0 g (0.36 mole) of tetrabromo-bisphenol A-bis (4-methoxycarbonylbenzyl)-ether were introduced into a spherical flask equipped with a stirrer and gas inlet tube. After the addition of 0.12 g of the titanate of 2-ethyl-1,3-hexane diol, transesterification was carried out at a temperature increasing from 1700 C to 2000 C. After the elimination of methanol had stopped, 6.64 g (0.04 mole) of isophthalic acid were added, followed by esterification for 30 minutes at 2000 C. 69.6 g (0.6 mole) of fumaric acid and 0.08 g of 2,4-ditert.-butylcresol were then added, followed by condensation for 30 minutes at 2000 C.

After 0.1 g of the zirconate of 2-ethyl-1,3-hexane diol has been added, polycondensation was carried out for 3.5 hours at a temperature of 2100 C.

A UP-resin was obtained with a bromine content of approximately 29% by weight and a molecular weight of 3400, as determined by gel chromatography.

60 parts by weight of the UP-resin were dissolved in 40 parts by weight of styrene to form a transparent solution which was hardened in a mould in the same way as in Example 1 to form transparent, 4 mm thick panels.

The panel mouldings contained 17.4% of organically bound bromine and were found to be self-extinguishing in the Underwriters Laboratory (UL)-test in the absence of any fire-retarding, synergistically acting additives, such as Sub203 or phosphorus compounds; the UL-test classification was 94/VO.

The panel mouldings were found to have the following properties: Flexural strength: 118.9 N/mm2 Impact strength: 7.1 KJ/m2 Dimensional stability under heat according to Martens: 1160 C according to ISO/R 75; A: 128 C After storage for 30 days in 20% aqueous sodium hydroxide at 850 C, the panels were externally unchanged; the smooth surface did not show any cracks. The change in weight amounted to +0.05%1' and to +0.02%2). The flexural strength amounted to 101.5 N/mm2, so that the decrease in flexural strength was 14.6%.

EXAMPLE 17.

Tetrachlorobisphenol A-b is- (4-methoxycarbonylbenzyl) -ether (structural formula (4)) as acid component.

Following the procedure of Example 16, a UP-resin with a molecular weight of 3300, as determined by gel chromatography, was condensed from the following reaction components: 93.6 g (0.9 mole) of neopentyl glycol, 6.2 g (0.1 mole) of ethylene glycol, 198.6 g (0.3 mole) of tetrachlorobisphenol A-bis-(4-metho:xy carbonyl benzyl)-ether, 16.6 g (0.1 mole) of isophthalic acid and 69.6 g (0.6 mole) of fumaric acid. 60 parts by weight of the resin thus obtained were dissolved in 40 parts by weight of styrene and the resulting solution was hardened in the same way as des carried in Example 1 to form 4 mm thick panels with which were found to have the following properties: 108.9 N/mm Flexural strength: Impact strength: 7.9 RJ/m2 Dimensional stability under heat: according to Martens: 1180 C according to ISO/R 75; A: 1310 C After storage for 30 days in 20% aqueous sodium hydroxide solution at 850 C the panels were externally unchanged; they still had a smooth surface with no cracks.

The change in weight amounted to +0.03%'' and to +0.008%2'. The flexural strength had fallen only slightly to 102.3 N/mm2, i.e. by 6%.

EXAMPLE 18.

Tetrabromo-p-xylylene-bis- (4-methoxycarboaylphenyl) -ether (structural formula (5)) as acid component.

Following the procedure of Example 16, but with terephthalic acid dimethyl ester being present during the transesterfication stage, a UP-resin with a bromine content of approximately 19% and a molecular weight of 3500, as determined by gel chromato- graphy, was condensed from the components: 72.8 g (0.7 mole) of neopentyl glycol, 13.8 g (0.05 mole) of tetrachloro-m-xylylene glycol, 15.5 g (0.25 mole) of ethylene glycol, 130 g (0.18 mole) of tetrabromo-p-xylylene-bis-(4-methoxycarbonyphenyl)ether, 34.9 g (0.18 mole) of terephthalic acid dimethyl ester, 6.64 g (0.04 mole) of isophthalic acid and 69.6 g (0.6 mole) of fumaric acid.

50 parts by weight of the resin thus produced were dissolved in 50 parts by weight of styrene and the resulting solution was hardened in the same way as described in Example 1 to form 4 mm thick transparent moulded panels which were found to have the following properties: Flexural strength: 113.6 N/mm2 Impact strength: 9.3 KJ/m2 Dimensional stability under heat: according to Martens: 1080 C according to ISO/R 75; A: 121" C After storage for 30 days in 20% aqueous sodium hydroxide solution at 850 C, the panel mouldings had only lost a little of their surface gloss; no cracks were present in the surface. The change in weight amounted to +0.08%i) and --0.03%2'. Flexural strength had fallen to 89.1 N/mm2, i.e. by 21.5%.

Part of the styrene/UP-resin solution was hardened in the presence of 6% by weight of Sb2O, form a 2 mm thick panel which had a bromine content of approxi- mately 9%. The panel was found to have self-extinguishing properties i.e. a classification of 94/VO according to the UL-test.

EXAMPLE 19.

Tetrabromo-p -xylylene-bis (4-methoxycarhonylphenyl) -ether (structural formula (5)) as acid component.

Following the procedure of Example 18, a UP-resin with a bromine content of approximately 31% by weight and a molecular weight of 3600, as determined by gel chromatography, was condensed from the components: 98.8 g (0.9 mole) of neopentyl glycol, 22.7 g (0.05 mole) of tetrabrom-m-xylylene glycol, 260 g (0.36 mole) of tetrabromop-xylylene-bis- (4-methoxycarbonylphenyl ) -ether, 14.9 g (0.09 mole) of isophthalic acid an

EXAMPLE 20.

The following constituents were weighed into a 500 ml two-necked flask equipped with a stirrer and reflux condenser: 29.4 g (0.035 mole) of the bis-methyl ester of structural formula 4 derived from tetrabromobisphenol A, 187.2 g (0.965 mole) of terephthalic acid dimethyl ester (DMT), 126 g (1.4 moles) of 1,4-butane diol and 0.07 g of the titanate of 2-ethyl-1,3-hexane diol. This mixture was transesterified for 4 hours at a temperature increasing from 160 to 1800 C. After the elimination of methanol had stopped, the temperature was increased in stages to 2500 C over a period of 2 hours; the pressure was reduced in stages to an optimum value of approximately 1 Torr. It was found that the reaction by which the viscous polyester mixture was formed could be terminated only 1 hour after the optimum reduced pressure had been reached. The copolyester which had formed hardened on cooling to form an opaque, tough, substantially colourless mass with a pale yellow tinge. The ?sp/e was 1.2 and the bromine content 4.58%. The weight losses as determined by thermogravimetric analysis (TGA) in air at a heating rate of 8 degrees C/minute amounted to 1% at 3360 C, to 5% at 3570 C, to 10% at 365" C and to 20% at 375" C.

A summary of other properties of the copolyester is given in Table 4.

EXAMPLE 21.

Following the same procedure as in Example 20, a copolyester with an ,2sp/c of 0.94 and a bromine content of 6.26%, as determined by elemental analysis, was produced from the following condensation reaction components: 42 g (0.05 mole) of the bis-methyl ester of structural formula (4) derived from tetrabromobisphenol A, 184 g (0.95 mole) of DMT, 126 g (1.4 moles) of 1,4-butane diol and 0.08 g of the titanate of 2-ethyl-1, 3-hexane diol. Some other properties of the copolyester are shown in Tables 4 and 5.

EXAMPLE 22.

The following reaction components were mixed 36.1 g (0.05 mole) of the bismethyl ester of structural formula (5) (having a bromine content of 41,96% and a chlorine content of 1.63%, and with para-substitution of the xylylene radical and of the unhalogenated terminal nuclei), 184.3 g (0.95 mole) of DMT, 126 g (1.4 moles) of 1,4-butane diol and 0.06 g of the titanate of 2-ethyl-1,3-hexane diol. The mixture was initially transesterified for 4 hours in a polycondensation vessel at a temperature increasing from 170 to 1900 C. Subsequently, polycondensation in vacuo at a temperature rising from 225 C to 2500 C was carried out until a product with an nsp/c of 0.96 was obtained.

The copolyester, which crystallised on cooling into an opaque mass, was substantially colourless. The bromine content, as determined by elemental analysis, was 6.07%; the chlorine content amounted to 0.3%; the weight loss (as determined by TGA; heating rate 8 degrees C/minute) amounted to 1% at 3490 C, to 5% at 3670 C, to 10% at 3750 C and to 20% at 3840 C.

Some other properties are shown in Tables 4 and 5.

EXAMPLE 23.

Following the procedure of Example 22, a bromine-containing copolyester (11Sp/C 1.35) was polycondensed from the following condensation components; 25.3 g (0.035 mole) of the same bis-ester as was used in Example 22, 187.2 g (0.965 mole) of DMT, 126g (1.4 moles) of 1,4-butane diol and 0.05 g of tetrabutyl titanate.

The copolyester, which crystallised on cooling into an opaque mass, was substantially colourless and, externally, was indistinguishable from a pure polytetramethylene terephthalate (PTMT) produced for comparison purposes (Comparison Example 28).

The copolyester had a bromine content of 4.4% and a chlorine content of 0.2%.

The weight loss as determined by TGA (in air; heating rate 8 degrees C/minute) amounted to 1% at 348" C, to 5% at 368" C, to 10% at 3770 C and to 20% at 3860 C.

Some other properties are set out in Tables 4 and 5.

EXAMPLE 24.

17.6 g of the bis-methyl ester of structural formula (4) derived from tetrabromobisphenol A, 7.56 g (0.084 mole) of 1,4-butane diol and 0.01 g of tetrabutyl titanate were weighed into a reaction vessel and transesterified for 2 hours at 180 to 2000 C while a gentle stream of nitrogen was passed over. Following the addition of 127.5 g of oligomeric butylene terephthalate (OBT) having the characteristics given in Example 25, the temperature was increased in stages to 2400 C with a gradual increase in the applied vacuum (i.e. reduction in pressure). Polycondensation was over after 1 hour at the optimum vacuum and at 2400 C.

The copolyester produced (sp/c=0.98) crystallised on cooling to form an opaque mass with a pale yellow tinge. It had a bromine content of 4.68%.

The weight losses according to TGA (in air; heating rate 8 degrees C/minute) were as follows: 1% at 3370 C; 5% at 3580 C; 10% at 3670 C and 20% at 3300 C.

Other properties are set out in Table 4.

EXAMPLE 23.

127.5 g of oligomeric butylene terephthalate (OBT) with an OH-number of 10S, an acid number of 2.7 and an 11sp/c of 0.15 (corresponding to a number average molecular weight (M,) of about 2500) and 15.25 g (0.021 mole) of the same bisester as was used in Example 22 were introduced into a polycondensation vessel together with 0.04 of tetrabutyl titanate. Transesterification was carried out for 2 hours at a temperature increasing from 200 to 2250 C while a gentle stream of nitrogen was passed over. The temperature was increased in stages to 2400 C and the vacuum was increased (i.e. pressure was reduced). A viscous copolyester melt was formed after 2 hours at the optimum vacuum and at 2400 C.

The copolyester, which crystallised on cooling into an opaque mass, was substantially colourless and, visually, was indistinguishable from the pure PTMT of Com- parison Example 28.

The bromine content as determined by elemental analysis was 4.6%; chlorine content 0.16%. The reduced specific viscosity (sp/c) was 1.1. The weight loss according to TGA amounted to 1% at 3330 C, to 5% at 3640 C, to 10% at 3740 Candot20% at 3830 C.

Some other properties are set out in Table 4.

EXAMPLE 26.

Following the procedure of Example 25, a copolyester with an 71sp/c value of 0.83, a bromine content of 6.1% and a chlorine content of 0.035%, was produced from 125.4 g of OBT with an OH-number of 105, an acid number of 2.7 and a rsp/c value of 0.15, and 21.66 g (0.03 mole) of the same bis-ester as was used in Example 22 in the presence of 0.07 g of the titanate of 2-ethyl-1,3-hexane diol as catalyst.

After crystallisation, the copolyester was in the form of an opaque, colourless mass which, externally, was indistinguishable from the pure PTMT produced in accordance with Comparison Example 28.

EXAMPLE 27.

43.3 g (0.06 mole) of the same bis-ester as was used in Example 22 and 43.5 g (0.48 mole) of 1,4-butane diol, together with 0.05 g of the titanate of 2-ethyl-1,3hexane diol as catalyst were weighed into a reaction vessel and transesterified for 2 hours at a temperature increasing from 180 to 2000 C while a gentle stream of nitrogen was passed over. Following the addition of 250.8 g of OBT (with the characteristics given in Example 25), the temperature was increased in stages to 2400 C with gradual increase in the vacuum (reduction in pressure). The polycondensation reaction was over 3 hours after the addition of the OBT. The copolyester which was produced (,isp/c 1.20) crystallised on cooling into an opaque, colourless mass which, externally, was indistinguishable from the pure PTMT of Comparison Example 28.

The copolyester had a bromine content of 6.17% and a chlorine content of 024%.

The weight losses according to TGA were as follows: 1% at 3380 C, 5% at 3640 C, 10% at 3740 C and 20% at 3820 C.

Some other properties are set out in Table 4.

Comparison Example 28.

(Production of PTMT as comparison material).

194 g (1 mole) of DMT and 126 g (1.4 moles) of 1,4-butane diol, together with 0.1 g of the titanate of 2-ethyl-1,3-hexane diol as catalyst, were weighed into a twonecked flask equipped with a stirrer. Transesterification was then carried out over a period of 4 hours at 180 to 1900 C while a gentle stream of nitrogen was passed over. The temperature was increased in stages to 2250 C, the pressure was reduced and the temperature was further increased to 2500 C with an increasing vacuum.

Polycondensation was over after 1 hour at the optimum vacuum and at a temperature of 2500 C.

The PTMT crystallised on cooling into an opaque, colourless mass (n5p/C of the polyester 1.54). The weight losses according to TGA were as follows: 1% at 3510 C, 5% at 3730 C, 10% at 3810 C and 20% at 390 C. Some other properties are shown in Tables 4 and 5 as comparison with those of the bromine-containing polyesters according to the invention.

EXAMPLE 29.

50.5 g (0.07 mole) of the same bis-ester as was used in Example 22, 180.4 g (0.93 mole) of DMT and 155.0 g (2.5 moles) of ethylene glycol were weighed into a polycondensation vessel, followed by the addition of 0.2 g of Zn-acetate as transesterification catalyst. While a gentle stream of nitrogen was passed over, transesteri- fication was carried out over a period of 4 hours at a temperature increasing from 180 to 200 C, 0.4 ml of triphenyl phosphite and 0.25 g of a GeO2-solution (10 g of GeO2 in 120 ml of solution) were added and the reaction temperature was increased in stages through 2200 C and 2400 C to 2600 C. When the temperature reached 2600 C, the pressure was reduced and further reduced in stages. The polycondensation reaction was terminated after 3 hours at the optimum vacuum and at 2600 C.

The copolyester produced (tispft 1.06) was transparent, had a pale yellow tinge and was still X-ray amorphous even after tempering for 3 days at 1000 C. The glass transition temperature as determination by the differential thermoanalysis (DTA) method was 820 C.

After moulding into 1 mm thick panels at a temperature of 2600 C, the copolyester showed a decrease in ,1sp/c to 0.92 afrer storage for 14 days at room temperature in 30% H2SO4, and to 0.9 after storage for 14 days at room temperature in 10% NaOH. The change in weight after storage under the above-mentioned conditions in H2SO4 was +0.34%, and after subsequent drying over P2O5 was 0.05%; similarly, after storage in NaOH the change in weight was +48%, and after subsequent drying over P2Os was -0.16%.

The water absorption values, as determined at room temperature, were as follows: 0.44% after 7 days 0.48% after 14 days 0.63% after 28 days EXAMPLE 30.

The following condensation components were mixed: 101.3 g (0.14 mole) of the same bis-ester as was used in Example 22, 258.4 g (1.33 moles) of DMT, 176 g (1.63 moles) of neopentyl glycol and 114 g (1.84 moles) of ethylene glycol, and 0.15 g of lithium hydride as catalyst. The mixture was transesterified over a period of 1.5 hours at a temperature increasing to 150 to 2000 C in a reaction flask, while a gentle stream of nitrogen was passed through, 220.4 g (1.32 moles) of isophthalic acid and 0.9 ml of triphenyl phosphite were then added, followed by condensation for 30 minutes at 200 C and then for 30 minutes at 220 C. 0.6 g of a GeO2 solution (10 g of GeO2 in 120 ml of a mixture of ethylene glycol and triethylamine) were then added and the reaction temperature was increased in stages to 2700 C.

The pressure was reduced at 2600 C and further reduced in stages. The polycondensaw tion reaction was terminated after 3 hours at the optimum vacuum and at a temperature of 270 C. The copolyester hardened on cooling into a transparent, yellow amorphous mass having an #sp/c value of 0.96 and a glass temperature (as determined by the DTA method) of 70 C.

After moulding into 1 mm thick panels at 250 C, the copolyester showed a decrease in ,1sp/c to 0.91 after storage for 14 days at room temperature in 30% H2SO4, and to 0.93 after storage for 14 days at room temperature in 10% NaOH.

The changes in weight after storage under the above mentioned conditions were as follows: +0.23% after storage in H2SO4, -0.005% after drying over P2O5; +0.27% after storage in NaOH, -0.18% after drying over P2O5. The water absorption values as determined at room temperature were as follows: 0.31% after 7 days 0.40% after 14 days 0.75% after 28 days Comparison Example 31.

A polyethylene terephthalate (PETP) with #sp/c=1.17 was produced by the procedure described in Example 29 from the following condensation components: 115.8 g (0.6 mole) of DMT, 186.2 g (3 moles) of ethylene glycol, 0.2 g of Zn acetate as transesterification catalyst, 0.2 g of tetrabutyl titanate as polycondensation catalyst, and 0.2 ml of triphenyl phosphite as antioxidant. The opaque partially crystalline material which formed had a glass temperature (DTA-method) of 63" C.

After moulding into 1 mm thick panels at 2600 C, the PETP showed a reduction in ,1sp/c to 0.97 after storage for 14 days at room temperature in 30% H2SO4, and to 0.84 after storage for 14 days at room temperature in 10% NaOH. The changes in weight after storage under the above-mentioned conditions were as follows: +0.37% after storage in H2HO4, +0.02% after drying over P2O5; 0.26% after storage in NaOH, -0.9% after drying over P205.

EXAMPLE 32.

The copolyester of Example 20 with a bromine content of 4.58% was processed with 5% by weight of Sb2O3 in a double-scresv extruder. The strands which were run off were then granulated and injection-moulded to form test specimens measuring 1.6 X 12.7 X 128 mm for testing in accordance with the Underwriters Laboratories Test UL 94. Result: UL 94 VO/VO (before and after storage for 14 days at 700 C).

Weight loss after 7 days at 1500 C: 0.14%.

The material did not show any sign of having changed or formed a coating during-this thermal storage.

EXAMPLE 33.

The copolyester of Example 21 with a bromine content of 6.26% was processed with 4% by weight of Sub2 0, in a double-screw extruder to form strands which were then granulated. Test specimens formed from the granulate by injection moulding had values of VO/VO in the UL-94 test. Their weight loss after 7 days at 1500 C was 0.18%. The material did not show any sign of having changed or formed a coating during this thermal storage.

EXAMPLES 34 and 35.

The copolymers of Examples 22 and 23 with respective halogen contents of 6.07% and 4.4% of bromine and 0.3% and 0.2% of chlorine, were processed with 4 and 5% by weight, respectively, of Sub203 in a double screw extruder. The strands which were run off were then granulated and injection-moulded to form test specimens for the UL 94 test.

Result: Both specimens had a UL 94 classification of VO/VO Weight loss after 7 days at 1500 C: 0.16% for Example 34 (copolyester of Example 22) and 0.19% for Example 35 (copolyester of Example 23).

Neither material showed any sign of having changed or formed a coating during its storage under heat.

Comparison Example 36.

A mixture of 86% by weight of PTMT (7Xsp/c=1.28), 9% by weight of standard commercial-grade pentabromodiphenyl ether and 5% by weight of Sb2O, was processed in a double screw extruder. The strands which were run off were granulated and injection-moulded to form test specimens for the UL 09 test.

Result: UL 94 VO/VO (before and after storage for 14 days at 700 C).

Weight loss after 7 days at 1500 C: 3.4%; the material showed a thick white coating.

EXAMPLE 37.

Following the procedure of Example 22, a bromine-containing copolyester (sp/c 0.94) was polycondensed from the following condensation components: 25.3 g (0.035 mole) of the bis-methylester of structural formula (5) having a bromine con- tent of 41.42% and a chlorine content of 1.80%, with para-substitution of the xylylene radical and with ortho-substitution of the unhalogenated terminal nuclei), 187.2 g (0.965 mole) of DMT and 126 g (1.4 moles) of 1,4-butene diol, in the presence of 0.05 g of tetrabutyl titanate. The transesterification and polycondensation reaction velocities were substantially the same as in Example 22 and 23.

The copolyester, which crystallised on cooling into an opaque mass, was substantially colourless and, externally, was indistinguishable from the pure polytetramethylene terephthalate produced for comparison purposes (Comparison Example 28).

The weight losses according to TGA were as follows: 1% at 3300 C, 5% at 353" C and 10% at 3700 C (heating rate 8 degrees C/minute; in air).

The crystallisation behaviour is shown in Table 4.

Following the procedure of Example 22, a bromine-containing copolyester (X1sp/c=1.13) was polycondensed from the following condensation components: 36.1 g (0.05 mole) of the same bis-ester as was used in Example 37, 184.3 g (0.95 mole) of DMT and 126 g (1.4 mole) of 1,4-butane diol, in the presence of 0.06 g of the titanate of 2-ethyl-1,3-hexane diol. The transesterification and polycondensation reaction velocities were substantially the same as in Example 22.

The copolyester, which crystallised on cooling into an opaque mass, was substantially colourless.

The weight losses according to TGA (heating rate 8 degrees C/minute; in air) were as follows: 1% at 330 C, 5% at 347" C and 10% at 3580 C.

The crystallisation behaviour is summarised in Table 4.

TABLE 4: Melting and crystallisation behavious according to measurements by DTA) of the bromine containing linear copolyesters according to the invention based on butane diol, DMT and the bis-esters (BE) of structural formulae (4) and (5) and of PTMT.

Degree of Melting Crystallisation Seed-forming rate crystallisation Crystallisation Acid component temperature temperature (super-cooling) (area of melting rate (width of the Example (mole % or g) Ts 2) Tk 2) Ts - Tk peak) crystal peak) 3) 28 (Comparison-PTMT) 100 DMT 229 C 189 C 40 C 5.5 cm 2.5 mins 20 96.5 DMT + 223 C 183 C 40 C 5.0 " 3.25 " 3.5 BE (4) 21 95 DMT + 22 C 183 C 39 C 5.5 " 3.0 " 5 BE (4) 22 95 DMT + 221 C 183 C 38 C 4.8 " 3.5 " 5 BE (5-p) 23 96.5 DMT + 224 C 186 C 38 C 6.0 " 3.0 " 3.5 BE (5-p) 24 127.5g OBT + 225 C 186 C 39 C 7.2 " 3.25 " 17.6g BE (4) 25 127.5g OBT + 225 C 181 C 44 C 5.0 " 3.75 " 15.2g BE (5-p) 27 250.8g OBT + 223 C 176 C 47 C 6.0 " 3.75 " 43.3g BE (5-p) 37 96.5 DMT + 221 C 182 C 39 C 5.0 " 3.25 " 3.5 BE (5-o) 38 95 DMT + 216 C 177 C 39 C 4.9 " 3.25 " 5 BE (5-o) TABLE 5 Resistance to hydrolysis of the bromide-containing linear copolyesters according to the invention based on butane diol, DMT and the bis-esters (BE) of structural formula (4) or (5), and of PTMT, as determined by storing 1 mm thick moulded panels in water, sulphuric acid or sodium hydroxide.

Acid component ) Halogen content Hydrolysis # sp/c 5) after Example (mole %) of the polyesters conditions 4) storage time of %Br %Cl 0 14 28 days 28 Comparison- PTMT) 100 DMT 0 0 Water, 80 C 1.54 1.12 0.76 " " " H2SO4, 50 C 1.54 1.24 1.12 " " " NaOH, 50 C 1.54 1.18 1.06 21 95 DMT+5 BE(4) 6.26 0 Water, 80 C 0.94 0.85 0.80 " " " H2SO4, 50 C 0.94 0.90 0.82 " " " NaOH, 50 C 0.94 0.92 0.87 22 95 DMT+5 BE (5-p) 6.07 0.3 Water, 80 C 0.96 0.84 0.78 " " " H2SO4, 50 C 0.96 0.92 0.94 " " " NaOH, 50 C 0.96 0.91 0.90 23 96.5 DMT+3.5 BE (5-p) 4.40 0.2 Water, 80 C 1.32 1.22 1.16 " " " H2SO4, 50 C 1.35 1.29 1.26 " " " NaOH, 50 C 1.35 1.24 1.19 Footnotes to Tables 4 and 5.

1) Measurements in air at a heating rate of 8 degrees C/minute up to 2600 C, and then at a cooling rate of 4 degrees C/minute; the amount weighed was 30 mg.

2) Temperature of the peak maxima.

3) Period of time elapsing from the beginning to the end of the crystallisation processes at a constant cooling rate of 4 degrees C/minute.

4) 30% by weight aqueous sulphuric acid; 10% by weight aqueous sodium hydroxide.

5) fisp/c measured in phenol/o-dichlorobenzene at 25 C: 1% solution.

BE (4)=bis ester of structural formula (4) derived from tetrabromobisphenol A.

BE (5-p)=bis-ester of structural formula (5) with para-substitution of the xylene radical and of the terminal nuclei.

BE (5-o)=bis-ester of structural formula (5) with para-substitution of the xylylene radical and with orthosubstitution of the terminal nuclei.

Claims (75)

WHAT WE CLAIM IS:

1. A polyester containing structural units of the formula

in which R' represents an alkylene radical (as hereinhef ore defined) having from 2 to 10 carbon atoms, a cycloalkylene radical or a divalent radical derived from a hydroxyl groupterminated oligomeric alkylene terephthalate, and in which the divalent radicals R include (a) radicals having the general formula

wherein X independently represents hydrogen, bromine or chlorine and Z represents

and, optionally, (b) radicals which are unsaturated, with the proviso that in the case where R does not include unsaturated radicals at least one of the substituents X of general formula (15) represents bromine.

2. A polyester containing structural units of the formula

in which R' represents an alkylene radical (as hereinbefore defined) having from 2 to 10 carbon atoms, a cycloalkylene radical or a divalent radical derived from a hydroxyl group-terminated oligomeric alkylene terephthalate, and in which the divalent radicals R include radicals having the general formula

wherein Z represents

or radicals having the general formula

wherein X in formulae (14) and (15) independently represents hydrogen, bromine or chlorine, with the proviso that in formula (15) at least one X represents bromine.

3. A polyester according to claim 1 or 2 wherein from 1 to 100 ml % of the divalent radicals R have the formula (14) or (15).

4. A polyester according to claim 3 wherein from 2 to 10 mol % of the divalent radicals R have the formula (14) or (15).

5. A polyester according to claim 3 wherein 100 mol % of the divalent radicals R have the formula (14) or (15).

6. A polyester according to claim 1 or 2 wherein up to 99 mol % of the divalent radicals R comprise phenylene radicals and/or naphthylene radicals and/or alkylene radicals containing from 3 to 10 carbon atoms and/or cycloalkylene radicals.

7. A polyester according to claim 6 wherein from 90 to 98 mol % of the divalent radicals R comprise phenylene radicals and/or naphthylene radicals and/or alkylene radicals containing from 3 to 10 carbon atoms and/or cycloalkylene radicals.

8. A polyester according to any one of the preceding claims which has a reduced specific viscosity of from 0.5 to 2.5.

9. A polyester according to claim 8 which has a reduced specific viscosity of from 0.8 to 1.6.

10. A polyester according to claim 1 or 2 which contains halogen atoms and is completely saturated.

11. A polyester containing structural units of the formula

in which R' represents an alkylene radical (as hereinbefore defined) having from 2 to 10 carbon atoms, a cyclealkylene radical or a divalent radical derived from a hydroxvl group-terminated oligomeric alkylene terephthalate, and in which the divalent radicals R include (a) radicals having the general formula

wherein X independently represents hydrogen, bromine or chlorine and Z represents

and (b) radicals which are unsaturated.

12. A polyester according to claim 1 or 11 wherein the unsaturated divalent radicals R are ethenylene radicals.

13. A polyester according to claim 1, 11 or 12 wherein the divalent radicals R include from 2 to 100 mol /^ of radicals having the formula (14) or (15), based on the amount of saturated radicals R.

14. A polyester according to claim 13 wherein the divalent radicals R include from 5 to 80 mol % of radicals having the formula (14) or (15), based on the amount of saturated radicals R.

15. A polyester according to any one of claims 1 and 11 to 14 which has a molecular weight of from 1000 to 6000.

16. A polyester according to claim 15 which has a molecular weight of from 2,500 to 4000.

17. A polyester according to any one of claims 1 and 11 to 16 which has a reduced specific viscosity of from 13 to 26 (ml/g).

18. A polyester according to any preceding claim where each X of formula (14) or each X of the central nucleus of formula (15) represents a bromine atom.

19. A polyester according to any one of claims 1 to 17 wherein each X of formula (14) or each X of the central nucleus of formula (15) represents a chlorine atom.

20. A polyester according to any one of claims 1 to 17 wherein the four substituents X of formula (14) or the central nucleus of formula (15) include both bromine and chlorine atoms.

21. A polyester according to any one of claims 1 to 17 wherein the four substituents X of the central nucleus of formula (15) include on average from 4.0 to 2.8 bromine atoms and from 0 to 1.2 chlorine atoms.

22. A polyester according to any one of claims 1 to 17 wherein the four substituents X of formula (14) or the central nucleus of formula (15) include on average from 4.0 to 3.0 bromine atoms and from 0 to 1.0 chlorine atoms.

23. A polyester according to any one of the preceding claims wherein the terminal phenylene groups of formula (14) or (15) are para substituted.

24. A polyester according to any one of the preceding claims wherein R' represents the alkylene radical of neopentyl glycol, ethylene glycol, 1,2-propane diol, 1,3butane diol or 1,4-butane diol.

25. A polyester according to any one of claims 1 to 23 wherein R' represents the alkylene radical (as hereinbefore defined) of diethylene glycol.

26. A polyester according to any one of claims 1 to 23 wherein R' represents the radical of 1,4-bis-(hydroxy methyl)-cyclohexane.

27. A polyester according to any one of claims 1 to 23 wherein R' represents the alkylene radical (as hereinbefore defined) of meta or para xylylene glycol.

28. A polyester according to any one of claims 1 to 23 wherein R' represents the alkylene radical (as hereinbefore defined) of meta or para tetrabromo or tetrachloro xylylene glycol.

29. A polyester according to any one of claims 1 to 23 wherein the hydroxyl group-terminated oligomeric alkylene terephthalate has a reduced specific viscosity of from 0.05 to 0.5.

30. A polyester according to claim 29 wherein the hydroxyl group-terminated oligomeric alkylene terephthalate has a reduced specific viscosity of from 0.1 to 0.2.

31. A polyester according to any one of claims 1 to 23, 29 and 30 wherein the alkylene radical of the hydroxyl group-terminated oligomeric alkylene terephthalate is ethylene, propylene or straight chain or branched butylene.

32. A polyester according to any one of the preceding daims which has a halogen content of from 1 to 30% by weight.

33. A polyester according to claim 32 which has a halogen content of from 3 to 10% by weight.

34. A polyester according to claim 11 substantially as described in any one of Examples 1 to 19.

35. A polyester according to claim 2 substantially as described in any one of Examples 20 to 27, 29, 30, 37 and 38.

36. A process for producing a polyester containing structural units of the formula

in which R' represents an alkylene radical (as hereinbefore defined) having from 2 to 10 carbon atoms, a cycloalkylene radical or a divalent radical derived from a hydroxyl group-terminated oligomeric alkylene terephthalate, and in which the divalent radicals R include (a) radicals having the general formula

wherein X independently represents hydrogen, bromine or chlorine and Z represents

and, optionally, (b) radicals which are unsaturated, with the proviso that in the case where R does not include unsaturated radicals at least one of the substituents X of general formula (15) represents bromine, which process comprises condensing (i) a dicarboxylic acid component comprising (a) a saturated dicarboxylic acid of formula HOOC--RR-COOH (12) or an ester forming derivative of such a saturated dicarboxylic acid, and, optionally, (b) an unsaturated dicarboxylic acid or ester forming derivative thereof, and (ii) a dihydric alcohol component comprising a saturated alcohol of formula HO-R'-OH (13), to form the desired polyester.

37. A process for producing a polyester containing structural units of the formula

m which R' represents an alkylene radical (as hereinbefore defined) having from 2 to 10 carbon atoms, a cycloalkylene radical or a divalent radical derived from a hydroxy group-terminated oligomeric alkylene terephthalate, and in which the divalent radicals R include radicals having the general formula

wherein Z represents

or radicals having the general formula

wherein X in formulae (14) and (15) independently represents hydrogen, bromine or chlorine, with the proviso that in formula (15) at least one X represents bromine, which process comprises condensing (i) a dicarboxylic acid component comprising a saturated dicarboxylic add of formula HOOC--RR-COOH (12) or an ester forming derivative of such a saturated dicarboxylic acid, and (ii) a dihydric alcohol component comprising a saturated alcohol of formula HO--R''-OH (13), to form the desired polyester.

38. A process for producing a polyester containing structural units of the formula

in which R' represents an alkylene radical (as hereinbefore defined) having from 2 to 10 carbon atoms, a cycloalkylene radical or a divalent radical derived from a hydroxyl group-terminated oligomeric alkylene terephthalate, and in which the divalent radicals R include (a) radicals having the general formula

wherein V independently represents hydrogen, bromine or chlorine and Z represents

and (b) radicals which are unsaturated, which process comprises condensing (i) a dicarboxylic acid component comprising (a) a saturated dicarboxylic acid of formula HOO > RCOOH (12) or an ester forming derivative of such a saturated dicarboxylic acid, and (b) an unsaturated dicarboxylic acid or ester forming derivative thereof, and (li) a dihydric alcohol component comprising a saturated alcohol of formula HO--R''-OH (13), to form the desired polyester.

39. A process according to claim 36 or 38 wherein the unsaturated dicarboxylic add or derivative is maleic acid, maleic anhydride or fumaric acid.

40. A process according to any one of claims 36 to 39 wherein the dicarboxylic acid component comprises as ester forming derivative of the saturated dicarboxylic acid, an ester compound having the formula

in which R" represents an alkyl radical having up to 6 carbon atoms.

41. A process according to any one of claims 36 to 39 wherein the dicarboxylic acid component comprises, as ester forming derivative of the saturated dicarboxylic acid, an ester compound having the formula

in which R" represents an alkyl radical having up to 6 carbon atoms.

42. A process according to claim 40 or 41 wherein the terminal phenylene groups of formula (4) or (5) are para-substitutei

43. A process according to claim 40, 41 or 42 wherein R" represents an alkyl radical having up to 4 carbon atoms.

44. A process according to claim 43 wherein R" represents a methyl or ethyl radical.

45. A process according to any one of claims 36 to 44 wherein each X of formula (14) or (4) or each X of the central nucleus of formula (15) or (5) represents a bromine atom.

46. A process according to any one of claims 36 to 44 wherein each X of formula (14) or (4) or each X of the central neucleus of formula (15) or (5) represents a chlorine atom.

47. A process according to any one of claims 36 to 44 wherein the four substituents X of the nucleus of formula (14) or (4) or the central nucleus of formula (15) or (5) include both bromine and chlorine atoms.

48. A process according to any one of claims 36 to 44 wherein the four substituents X of the central nucleus of formula (15) or (5) include on average from 4.0 to 2.8 bromine atoms and from 0 to 1.2 chlorine atoms.

49. A process according to any one of claims 36 to 44 wherein the four sub stituents X of the nucleus of formula (14) or (4) or the central nucleus of formula (15) or (5) include on average from 4.0 to 3.0 bromine atoms and from 0 to 1.0 chlorine atoms.

50. A process according to any one of claims 36 to 49 wherein the dicarboxylic acid component additionally comprises terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, adipic acid, azeleic add, sebacic acid, cyclobutane dicarboxylic acid, cyclopentane dicarboxylic acid, cyclohexane dicarboxylic acid, cyclohexylene diacetic acid or ester forming derivatives thereof or mixtures thereof.

51. A process according to any one of claims 36 to 50 wherein the dicarboxylic acid component additionally comprises orthophthalic add, tetrahydrophthalic add, endomethylene tetrahydrophthalic acid or hexachloroendomethylene tetrahydrophthalic acid or ester forming derivatives thereof or mixtures thereof.

52. A process according to any one of claims 36 to 51 wherein the dihydric alcohol component comprises ethylene glycol, diethylene glycol, neopentyl glycol, 1,2-propane diol, 1,3-butane diol, 1,4-butane diol, 1,4-bis-(hydroxy methyl)cyclo- hexane, meta or para xylylene glycol, meta or para tetrachloro or tetrabromo xylylene glycol, or mixtures thereof.

53. A process according to any one of claims 36 to 52 wherein the dihydric alcohol component comprises a hydroxyl group-terminated oligomeric alkylene terephthalate having a reduced specific viscosity of from 0.05 to 0.5.

54. A process according to claim 53 wherein the dihydric alcohol component comprises a hydroxyl group-terminated oligomeric alkylene terephthalate having a reduced specific viscosity of from 0.1 to 0.2.

55. A process according to any one of claims 36 to 54 wherein the alkylene group of the hydroxyl groups-terminated oligomeric alkylene terephthalate is ethylene or butylene.

56. A process according to any one of claims 36 to 55 wherein the dicarboxylic add component and the dihydric alcohol component are condensed in a molar ratio of from 1:1.1 to 1:1.5.

57. A process according to claim 56 wherein the dicarboxylic acid component and the dihydric alcohol component are condensed in a molar ratio of from 1:1.2 to 1:1.4.

58. A process according to any one of claims 36 to 57 wherein the condensation is carried out by first transesterifying the add and alcohol components in the presence of a transesterification catalyst, and then polycondensing the transesterification product in the presence of a polycondensation catalyst.

59. A process according to claim 38 substantially as described in any one of Examples 1 to 19.

60. A process according to claim 37 substantially as described in any one of Examples 20 to 27, 29, 30, 37 and 38.

61. A polyester whenever produced by the process according to claim 37 or 60 or to any one of claims 40 to 58 when appendant to claim 37.

62. A polyester whenever produced by the process according to claim 38, 39 or 59 or to any one of claims 40 to 58 when appendant to claim 38.

63. A composition comprising an unsaturated polyester according to any one of claims 11 to 17 and 34, or any one of claims 18 to 33 when appendant to any one of claims 11 to 17, or claim 62, and a monomer which is copolymerisable therewith.

64. A composition according to claim 63 wherein the monomer is styrene.

65. A composition according to claim 63 substantially as described in any one of Examples 1 to 19.

66. A flame retarded composition comprising a polyester according to any one of claims 1 to 35, 61 and 62 or a composition according to claim 63, 64 or 65, and a flame retarding agent.

67. A flame retarded composition according to claim 66 wherein the flame retarding agent is a compound of antimony or boron.

68. A flame retarded composition according to claim 67 wherein the flame retard ing agent is antimony trioxide.

69. A flame retarded composition according to claim 66, 67 or 68 wherein the flame retarding agent is present in an amount of from 2 to 12% by weight, based on the total weight of the flame retarded composition.

70. A flame retarded composition according to claim 69 wherein the flame retarding agent is present in an amount of from 4 to 7% by weight, based on the total weight of the flame retarded composition.

71. A flame retarded composition according to claim 66 substantially as described in Example 18.

72. A flame retarded composition according to claim 66 substantially as described in Example 32, 33, 34 or 35.

73. A moulding composition comprising a polyester according to any one of claims 1 to 35, 61 and 62, a composition according to claim 63, 64 or 65, or a flame retarded composition according to any one of claims 66 to 72, and a filler and/or pigmenting agent and/or a mould release agent.

74. A moulding composition according to claim 73 wherein the filler comprises glass fibres.

75. A moulding composition according to claim 74 which comprises from 2 to 60% by weight of glass fibres, based on the weight of the moulding composition.