GB2131819A - Process for the preparation of polymethacrylamide and copolymers thereof - Google Patents

Abstract

A process for the preparation of polymethacrylamide or copolymers thereof in solid form comprises copolymerising in an aqueous melt methacrylamide and optionally other water-soluble monomers copolymerisable therewith, the monomers comprising from 20 to 90% by weight of the aqueous melt, copolymerisation being effected by radicals at a temperature of from 20 DEG to 90 DEG C on a thermogulatable substrate and in a layer from 1 to 10 cm thick, and if necessary waiting until the desired level of solidification is attained. UV polymerization is preferred. The polymers prepared according to the invention are useful as flocculating aids.

Description

SPECIFICATION Process for the preparation of polymethacrylamide and copolymers thereof This invention relates to a process for preparing polymethacrylamide and copolymers thereof. More particularly it relates to a process for preparing polymethacrylamide and copolymers thereof in solid form from aqueous melts.

In order to aid the precipitation of sludges in an aqueous medium, various types of flocculating aids based on polymers have been developed.

These generally have to be water-soluble. The various types of substances to be precipitated make it necessary to use different types of flocculating aids based on polymers. Thus, nonionogenic polymers maybe used as flocculating aids in some circumstances whilst ionogenic polymers (polyelectrolytes) having functional groups suitable for an exchanging effect may be used in others. Major examples of non-ionogenic polymeric flocculating aids are the polyacrylamides and partially saponified ionogenic polyacrylamides or copolymers of acrylamides with vinylcarboxylic acids.

In the literature, the monomers acrylamide and methacrylamide are frequently treated as being technically equivalent, even in connection with copolymers. If one looks at the product properties in the field of flocculating aids, for example, there is very little evidence of equivalence. On the basis of current knowledge, it is not possible to predict which flocculating aid will be specifically suitable for a particular application. (Cf. Uilmanns Encyklopadie der Technischen Chemie, 4th Edition, Volume 11, Verlag Chemie). The prevailing view is that high molecular masses (up to a magnitude of 107) promote the flocculating effect of polymers.In the interests of producing a high molecular weight polymer, olefinically unsaturated monomers have on the one hand to be polymerised in an aqueous solution (in order to eliminate the transfer function of organic solvents) and on the other hand at the lowest possible temperatures.

It is also convenient to use minimal quantities of free-radical initiators or to initiate polymerisation by high-energy radiation (e.g. UV). From DE OS 22 48 715, a process for preparing watersoluble acrylic polymers is known wherein a concentrated aqueous solution of the monomers is applied in the form of a layer or in droplet form to a fixed or movable support in the presence of a photopolymerisation accelerator and is then irradiated. The inventive feature is that an initiator which reinforces and completes the activity of the photopolymerisation accelerator is added to the aqueous solution, so as to produce acrylic polymers and copolymers having a lower molecular weight. Examples given include copolymers of acrylamide with acrylonitrile and/or acrylic acid, but not methacrylamide. Difficulties occur as a result of the tackiness of the products.

The application is directed,.inter alia, to the use of strips, particularly steel strips, the surface of which does not need to have a water-repellent finish. For polymerisation, the strips are cooled.

It has proved particularly difficult to polymerise or copolymerise methacrylamide to yield polymers of high molecular mass. In particular, uncontrolled imide formation during polymerisation generally reduces drastically the watersolubility. The imide formation is, as expected, favoured by elevated temperature and acid catalysis. (Cf. US Patent No. 2 486 190).

According to the prior art, it was to be expected that polymethacrylamides would be too inactive, below a certain molecular weight limit, to be useful in the field of flocculating aids. In any case, previous research has been directed towards high molecular weight solids, if possible capable of being ground, which can be converted into watersoluble high molecular products, e.g. after partial saponification, without any appreciable polymer decomposition. Hitherto, there has been no process available in the art which satisfies the requirements regarding the polymerisation of methacrylamide, possibly together with other comonomers, for the purposes mentioned, without involving serious limitations.It would also be desirable to find a reaction which would lead to a low residual monomer content, for example < 5% by weight (based on the total monomers), preferably < 0.5% by weight.

We have now devised a process which generally fulfils these requirements. The products obtainable according to the process of our invention are generally capable of being ground; they can also be converted into water-soluble high molecular products after partial saponification by aqueous alkali without any appreciable polymer decomposition. This property can also be used for further characterising the products of the process (see below).

According to the invention, therefore, we provide a process for the preparation of polymethacrylamide or copolymers thereof in solid form which comprises copolymerising in an aqueous melt methacrylamide and optionally other water-soluble monomers copolymerisable therewith, the monomers comprising from 20 to 90% by weight of the aqueous melt, copolymerisation being effected by radicals at a temperature of from 200 to 900 on a thermoregulatable substrate and in a layer from 1 to 10 cm thick, and if necessary waiting until the desired level of solidification is attained.

The process according to the invention relates primarily to the use of methacrylamide and also, as possible comonomers, to acrylamide, methacrylonitrile and acrylonitrile and other water-soluble monomers such as polymerisable acids and the salts thereof, particularly acrylic, methacrylic, maleic, fumaric and itaconic acid; hydroxy-group-containing esters of polymerisable acids, particularly the hydroxyethyl and hydroxypropyl esters of acrylic and methacrylic acid may also be used. It also relates to the use of esters and amides of polymerisable acids which contain amino and ammonium groups, such as the dialkylamino esters, particularly the dimethylaminoalkyl and diethylaminoalkyl esters of acrylic and methacrylic acid, and the trimethylammoniummalkyl and triethylammoniumalkyl esters and the corresponding amides.The watersoluble or hydrophilic comonomers will be referred to as type A comonomers. Minor amounts of cross-linking monomers such as, for example, monomers with more than one polymerisable group in the molecule, may also be copolymerised (type B comonomers).

To a lesser extent, water-insoluble comonomers may also be copolymerised, such as the esters of acrylic and/or methacrylic acid with C,~10 alcohols, styrene and alkylated styrenes (type C comonomers). Generally, the proportion of type A monomers is from 0 to 50% by weight, based on the total monomers. The proportion of cross-linking comonomers (type B) is from 0 to 5% by weight, preferably from 0.01 to 0.1% by weight, based on the total monomers. The waterinsoluble (hydrophobic) monomers of type C generally make up O to 10% by weight of the monomers.

The proportion of methacrylamide in the copolymers is generally between 50 and 100% by weight, and is preferably between 80 and 100% by weight. The proportion of the remaining comonomers depends on the intended application.

Examples of cross-linking monomers of type B include amides such as methylene-bis-acrylamide ormethacrylamide and also esters of polyols such as ethyleneglycol diacrylate or methacrylate, also vinylmethacrylate and allyl compounds such as allylmethacrylate, allylcyanurate and also crosslinkable monomers such as the N-methylol compounds of amides such as methacrylamide or acrylamide and the ethers derived therefrom.

The process according to the invention is carried out in an aqueous melt containing the monomers in a concentration of 20-90, particularly 40~70% by weight, based on the aqueous melt and in a temperature range of from 20 to 90 , preferably 50 to 800C. According to the prior art, such highly concentrated aqueous melts would appear to be totally unsuitable for the purposes of the present invention, owing to the tendency to cross-link which increases as the concentration and temperature increase. The process according to the invention is carried out using a thermoregulatable substrate, preferably with a non-metallic separating surface, whilst the layer thickness of the aqueous melt is from 1 to 10, preferably from 1 to 5 cm.The process may be carried out, for example, by strip polymerisation on non-metallic strips or strips with a non-metallic separating surface. Examples of non-metallic (polymeric) materials include (halogenated) polyolefins such as polytetrafluoroethylene, polyesters or polyamides.

Substances which may react as transfer agents are generally to be avoided if high molecular weights are desired. (It should, however, be pointed out that the chain length and hence the molecular weight can be regulated, i.e. generally lowered, with the aid of transfer agents or regulators). The influence of the regulators become apparent, for example, from the Examples. A suitable regulator might be, for example, formic acid, as in the process described in US Patent 4 361 687, or a sulphur regulator such as mercaptoethanol, thioglycolic acid, tetramercaptopentaerythritol, etc.

The content of regulators is generally between 0 and 5% by weight, preferably from 0.1 to 2% by weight, based on the monomers. The polymers or copolymers of methacrylamide prepared according to the invention may generally also be characterised by the fact that, after partial saponification of a 1.5% by weight suspension of the polymers in 0.5% sodium hydroxide solution for 90 minutes at 80 to 900C, a homogeneous solution is obtained having a viscoity lispecic of 0.1 to 150 dl/g [in a 0.01% saline solution ] .

Advantageously, the process is carried out as UV polymerisation in accordance with methods known per se. The UV source may be, for example, UV lamps of the OSRAM L 40-70 W type (radiation range 200-500 nm, maximum about 320-400 nm) or mercury vapour lamps, and best of all daylight. Conveniently, the polymerisation mixtures contain photosensitisers such as benzoin and benzoin derivatives such as benzoin ethers, e.g. benzoin-ethyl-propylether, and benzil derivatives such as benzilmethylketal.

Alternatively or in conjunction with the photosensitisers, it is also possible to use known radical initiators such as azo compounds, e.g. 2,2'- azobis-(isobutyronitrile), 2,2'-azobis-(isobutyric acid hydrazide), 2,2-azobis-(isobutyric acid amide), 2,2'-azobis-(ethylisobutyrate), 4,4'- azobis-14-cyanovaleric acid), 1,1 '-azobis-(cyclo- hexane-1 -nitrile), azobis-(isobutanol), azo-bis (isobutyl acetate) and per compounds such as ammonium persulphate, benzoyl-peroxide, tert.butylperpivalate etc., optionally several of these simultaneously. Generally, the content of photosensitiser is 0.001 to 1% by weight, preferably 0.01 to 0.1% by weight, based on the monomers used. The content of radical initiators is generally from 0.01 to 5% by weight, preferably between 0.1 and 3% by weight, based on the monomers.

Towards the end of the process according to the invention, there is a tendency for the mixtures to solidify, when applied in layer thicknesses of from 1 to 5 cm (solid gel). If this solid state does not occur during polymerisation itself, it generally occurs at the latest after 10 to 50 hours when left to stand in the air. High-energy drying operations are possible but are generally not necessary. The polymerisation process usually takes 1 to 24 hours, depending to some extent on the process parameters such as temperature, energy supply during irradiation, etc. The temperature range of 20 to 90, preferably 50 to 800C, envisaged according to the invention, can be maintained as mentioned above by the use of a thermoregulatable substrate.In practice, steel conveyor belts capable of being heated and cooled, preferably with a separating film of polyester, TEFLONs and polyamide, are used.

The following Examples serve to illustrate the process according to the invention.

The value for the viscosity ?1specic is determined according to Houben-Weyl "Methoden der Organischen Chemie", Volume 14/1, pages 81 to 84, Georg Thieme Verlag, Stuttgart, 1961, or according to DIN 51 562, DIN 1342 and DIN 7745. It has been found that the residual monomer content, when the process according to the invention is used, is < 0.5% by weight, based on the total monomers.

Example 1 Polymerisation of methacrylamide without a regulator At 500 C, methacrylamide is added in batches to permutite-treated water in a heatable agitator vessel until a 50% melt of methacrylamide is formed 500 ppm of benzoin ethyl ether, based on the solids are added to this melt as a 1% solution in dimethyl-formamide. Then the melt is applied in a 20 mm layer to a movable steel polymerisation strip tempered to 500C, with a polyester film 50 ym thick as a separating layer and irradiated at 30 cm intervals with intermittent UV lamps of the OSRAM L 40/70W type (radiation range 200-500 nm).Within 2 hours the melt polymerises to form a solid gel which is continuously removed from the polymerisation strip and, after 48 hours' storage at ambient temperature, dried to form a solid product which is 70~75% capable of being ground. After partial saponification (1.5%) in 0.5% NaOH for a period of 90 minutes at 80~90 C, a sample of this polymethacrylamide yields a homogeneous viscous solution with a degree of saponification of 11%, based on the polymethacrylamide used, and an X7speclC in 0.01% NaCI of 51 dl/g.

Example 2 Polymerisation of methacrylamide with regulator The same process was carried out as in Example 1, except that instread of 500 ppm of benzoin ethyl ether 1,000 ppm of benzoin ethyl ether and 1% of formic acid and 0.5% of mercaptoethanol were used, all based on the solids content. After saponification (degree of saponification 12%) an nspecic of 1.43 dl/g was obtained in 0.01% NaCI.

Example 3 Instead of benzoin ethyl ether as in Example 1, polymerisation was carried out with 700 ppm of Irgacure 651at made by Messrs Ciba-Geigy (benzildimethylketal), in 10% solution in dimethylformamide. After partial saponification; 71sPec/c values of 93 dl/g were obtained in a 0.01% NaCI solution.

Example 4 The same procedure was used as in Example 3, except that an additional 0.13% of formic acid and 0.13% of mercaptoethanol were added. After partial saponification, an 71spec/c value of 4.79 dl/g was obtained in 0.01% NaCI.

Example 5 The procedure used in Example 3 was followed except that an aqueous solution containing 50% by weight of a mixture consisting of 50 parts by weight of methacylamide and 50 parts by weight of acrylamide was used in place of acrylamide only. After partial saponification a viscosity Tispecic of 88 dl/g in 0.01- NaCI was obtained.

Example 6 The procedure used in Example 3 was followed except that an aqueous solution containing 80% by weight of a monomer mixture consisting of 50 parts by weight of methacrylamide and 50 parts by weight of trimethylammonium ethylmethacrylate chloride was used in place of methacrylamide only. After partial saponification a viscosity ?1specie of 48 dl/g in 0.01% NaCI was obtained.

Example 7 The procedure used in Example 3 was followed except that an aqueous solution containing 50% by weight of a monomer mixture consisting of 80% by weight of methacrylamide and 20 parts by weight of methacrylic acid was used in place of methacrylamide only. After partial saponification a viscosity Tispecic of 67.5 dl/g in 0.01% NaCI was obtained.

Example 8 The procedure used in Example 3 was followed except that an aqueous solution containing 50% by weight of a mixture consisting of 80% by weight of methacrylamide and 20% by weight of methyl methacrylate was used in place methacrylamide. After partial saponification a viscosity rlspecic of 46.3 g/dl in 0.01% NaCI was obtained.

Example 9 The procedure used in Example 3 was followed except that an aqueous solution containing 50% by weight of a mixture consisting of methacrylamide and 25 ppm based on methacrylamide of N,N-ethylen bis(methacrylamide) was used in place of methacrylamide. After partial saponification a viscosity Tispecic of 110 dl/g in 0.01% NaCI was obtained.

Example 10 The procedure used in Example 3 was followed except that an aqueous solution containing 50% by weight of a mixture consisting of 80 parts by weight of methacrylamide and 20 parts by weight of 2-hydroxy ethylmethacrylate was used in place of methacylamide. After partial saponification a viscosity VspeC/C of 50 dl/g in 0.01 NaCI was obtained.

Example 11 In place of the benzoin ethyl ether used in Example 1 the polymerization was carried out with 500 ppm benzoin (a-hydroxy benzylphenyl ketone) obtained from Fluka AG (Buchs, Switzerland) as a 10% solution in dimethylformamide. After partial saponification a viscosity lispecic of 66 dl/g in 0.01 NaCI was obtained.

Example 12 Portions of methacrylamide were introduced at 500C into "Permutite"-treated water in a heatable stirred vessel until a 50% methacrylamide melt had formed. 100 ppm of ammonium peroxydisulfate (APS), based on the solid, were added to this melt.

The melt was then deposited as a layer 20 mm thick on a moveable polymerization steel belt heated to 800C and provided with a 50 yam thick polyester film as a parting layer. The melt polymerized within 2 hours to a solid gel, which was continuously removed from the polymerization belt, maintained for 48 hours at room temperature and then dried to a 70~75% grindable solid product. After partial saponification of a 1.5% by weight sample in 0.5% NaOH for 90 minutes at 80-900C a homogenous viscous solution having a degree of saponification of 11% based on the polymethacrylamide used and a viscosity rlspecle of 51 dl/g in 0.01% NaCI was obtained.

Claims (14)

Claims

1. A process for the preparation of polymethacrylamide or copolymers thereof in solid form which comprises copolymerising in an aqueous melt methacrylamide and optionally other water-soluble monomers copolymerisable therewith, the monomers comprising from 20 to 90% by weight of the aqueous melt, copolymerisation being effected by radicals at a temperature of from 200 to 900C on a thermoregulatable substrate and in a layer from 1 to 10 cm thick, and if necessary waiting until the desired level of solidification is attained.

2. A process as claimed in claim 1 wherein the polymerisation is carried out on a thermoregulatable substrate with a non-metallic separating surface.

3. A process as claimed in claim 1 or claim 2, wherein after partial saponification of a 1.5% suspension of the product polymers in 0.5% sodium hydroxide solution for 90 minutes at 80 to 900C the products form a homogeneous solution with a viscosity 17speC/c of 0.1 to 150 dl/g (in 0.01% saline solution).

4. A process as claimed in any of claims 1,2 and 3, wherein the process is carried out continuously.

5. A process as claimed in any of claims 1 to 4, wherein the process is carried out as UV polymerisation.

6. A process as claimed in any of claims 1 to 5, wherein polymerisation is carried out in the presence of photosensitisers.

7. A process as claimed in claim 6, wherein the UV polymerisation is effected in the presence of benzoin, benzoin ethers or benzil derivatives.

8. A process as claimed in any of claims 1 to 7, wherein polymerisation is carried out in the presence of regulators.

9. A process as claimed in claim 8, wherein the polymerisation is carried out using formic acid.

10. A process as claimed in any of claims 1 to 9 wherein polymerisation is carried out in a layer 1-5 cm thick.

11. A process as claimed in any of claims 1 to 10 wherein the monomers comprise 40 to 70% by weight, of the aqueous melt.

12. A process as claimed in any of claims 1 to 11 wherein the water-soluble monomers copolymerisable with the metacrylamide are selected from acrylamide, methacrylonitrile, acrylonitrile, acrylic acid, methacrylic acid, fumaric acid, and itaconic acid, and esters of polymerisable acids, optionally containing hydroxyl groups, amino or ammonium groups.

13. A process as claimed in claim 1 substantially as hereinbefore described.

14. A process for the preparation of polymethacrylamide or copolymers thereof in solid form substantially as hereinbefore described with reference to any of the Examples.