GB2226322A - Block polymer compositions - Google Patents

Description

1 1 1.

z CASE 2967 "POLYMERIC COMPOSITIONS AND METHOD FOR PREPARING THEM" The present invention relates to Polymeric compositions comprising: a Linear copolymer constituted by four alternating blocks which can be represented by the formula (I) or (II):

B1-T-Aj-B2-A2 I o r Bi -Al -B2 -T-A2 I I w h e r e i n Al, A2 If B1 B2 and T respectively are 2 vinyLaromatic blocks, 2 dienic blocks and a portion of random copolymer formed by dienic and vinyLaromatic monomer units; and a copolymer constituted by two blocks, represented by the formulae (III) or (IV) B3 -T-A3 is o r B3 -A3 wherein: A3 is a polyvinylaromatic block different from, or equal to, Al block or A2 block; B3 is a polydienic block different from, -or equal to, B1 block or B2 block, and T represents the hereinabove seen random copolymer.

Also the processes for obtaining both of the above said components of said blend simultaneously and during the same process of synthesis fall within the scope of the present invention.

The polymeric compositions are endowed with very good characteristics of impact strength and processability, which can be ( I I I) (IV) combined with a high transparence, which make them suitable for all of the uses provided for the %1 2.

is transparent, impact resistant materiaLs.

During the past years, the bLock copoLymers obtained from the bLockcopoLymerization of conjugated dienic monomers with vinyLaromatic monomers, such as, e.g., the bLock copoLymers of poLybutadiene and poLystyrene, and the bLock copoLymers of poLyisoprene with poLystyrene, have shown a particuLar deveLopment. Such copoLymers can be used as such, i.e., in the same form as they are produced by the Living anionic copolymerization, as well as after their partiaL or totaL hydrogenation.

This is the case of the Linear bLock copoLymers constituted by aLternating bLocks of poLydienes and poLyvinyLarenes, with a particuLar structure and distribution of the individuaL bLocks, and having a structuraL formuLa of (I) or (II) type, which show an extremeLy favourabLe baLance of physicaL and mechanicaL characteristics. Such bLock copoLymers, as weLL as their derivatives, are discLosed by the present AppLicant in the U.K. Patent Application H.8726075 and in a co pending patent appLication.

The bLending of bLock copoLymers both with one another, and with impactresistant and non-impactresistant poLystyrene in order to achieve resins endowed with improved properties, is known from the prior art as w e L L.

Compositions and/or bLock copoLymers characterized by the use of poLymeric structures suitabLe for aLL of those uses for which transparent impact-resistant poLystyrene has been used in the past, or is stiLL being used at present, are reported, e.g,., in BP patent No.

1,130,1770; BP patent No. 1,335,077; and U.S. patent No.

3.

1 is 4,086,298.

However, the copolymers cLaimed in these references do not show an optimum baLance of rheoLogic properties, impact strength and transparency.

Such a baLance of properties is further modified by the possibLe use of poLystyrene which, if, on the one hand, enhances the opticaL characteristics, on the other hand decreases the impact strength of the so-obtained compositions.

The drawbacks which affect the prior art are overcome by the poLymeric compositions according to the instant invention, constituted by bLends of the two bLock copoLymers respectiveLy compLying with the generaL formuLae (I) or (II) and (III) or (IV), as hereinabove seen.

In accordance therewith, and according to a first aspect thereof, the present invention reLates to new poLymeric compositions comprising:

(a) from 40 to 90% by weight of a bLock copoLymer of generaL formuLa (I) or (II); (b) from 10 to 60% by weight of a bLock copoLymer of generaL formuLa (III) or (IV), wherein the symboLs Al, A2, A 3, Bi B2., B3 and T have the hereinabove seen meaning.

The poLymeric compositions according to the present invention are characterized in that the weight average moLecuLar weight of the fourbLock copoLymer of formuLa (1) or (II) is comprised within the range of from 50,000 to 300,000, whiLst the weight average moLecuLar weight of the two-bLock copoLymer is comprised within the range of from 20,000 to 150, 000.

4.

In the same compositions, the percentage by weight of the random bLock T is comprised within the range of from 5 to 50%, preferabLy of from 10 to 25%, as referred to the totaL of the two copoLymers which constitute the bLend.

In the same compositions, the totaL amount of vinyLaromatic monomeric units is comprised within the range of from 60 to 90% by weight, with the baLance to 100% being constituted by the dienic monomeric units.

In the above definitions, the bLocks Al, A2, A3 and Bl., S2 and S3 are practicaLLy pure bLocks; i.e., they are nearLy totaLLy constituted by vinyLarenic and dienic units.

In the preferred form of practicaL embodiment, the bLocks B1, B2 and B3 are poLystyrenic bLocks and T is a random styrene-butadiene copoLymer.

StiLL in the preferred form of practicaL embodiment, the totaL content of dienic units in the poLymeric composition is comprised within the range of from 20 to 30% by weight, and the weight average moLecuLar weight of the 4-bLock copoLymer is comprised within the range of from 100,000 to 200,000; and the weight average moLecuLar weight of the 2-bLock copoLymer is comprised within the range of from 40,000 to 100,000. To said compositions, another poLystyrenic resin, such as, e.g., poLystyrene or impact-resistant poLystyrene, can be added in such an amount as not to endanger the combination of properties of the binary composition.

PoLymeric compositions according to the present invention constitute a progress from the viewpoint of the properties, as compared to the bLock copoLymer of formuLa 1 - A 5.

(1) or (II), when considered on an individuaL basis.

The Linear bLock copoLymer constituted by 4 aLternating bLocks compLying with the generaL formuLa (I) or (II) according to the present invention can be obtained by poLymerization, by operating in an organic soLvent to which suitabLe amounts are optionaLLy added of an aLiphatic or cycLoaLiphatic poLar compound seLected from among ethers or amines, at temperatures comprised w i t h i n the range 0 f from 300C t 0 1500 C, and under pressures equaL to, or higher than, atmospheric pressure, in the presence of said aLkyL-metaL or aryL-metaL initiators, as customariLy used in the synthesis of poLymers according to the Living anionic poLymerization method.

Such a synthesis the U.K. Patent Application N.872GO75 route is disclosed reLating to the discLosure of such copoLymers and to the method for synthetizing them. The two-bLock copoLymers compLying with the above formuLae (III) or (IV) can be synthetized, on the contrary, according to methods as known from the prior art, as weLL as by means of the same process of synthesis as discLosed in the above said patent appLication, with the reaction being Limited to the first step. More particuLarLy, for the synthesis of the copoLymers of formuLa (III), metered amounts of butadiene and styrene are fed to a reactor as a mixture with one another, and the poLymerization is carried out in a soLution in a hydrocarbon, with a suitabLe initiator for the Living anionic poLymerization, untiL monomer conversion is compLete or substantiaLLy compLete; in this way, a Living two-bLock copoLymer 11 6.

preliminary feeding a The out according to the steam evaporating the The copolymer of polymerization, with monomers The constituents of the polymeric compositions according to the instant invention can be blended and compounded according to the modalities and routes as weLL-known from the prior art. So, e.g., the ingredients can be blended in the molten state and extruded or mixed in Banbury type mixers, or they can be blended as solutions. The present Applicant has also developed -and they constitute a further purpose of the present invention -- novel and original processes which make it possible the 2 components to be produced simultaneously and by means of one single synthesis process.

According to one of such processes, the synthesis is carried out according to the following steps:

(1) a first step during which a mixture is copolymerized in the presence of initiators, until the conversion of the monomers composed by a vi B3 -T-A3 is formed, which is constituted by non-pure blocks, i.e., by blocks Linked to each other by a copoLymeric portion of chain, constituted by randomly Linked monomeric units of butadiene and styrene.

The polymer formed is recovered after the quenching of the Living active centres, by compound having an acidic character.

recovery of the polymeric material is carried customary methods, such as, e.g., by solvent and drying the polymer.

formula (IV) is obtained by anionic the sequential addition of the the prior art.

according to is nearly nylaromatic complete, monomer which mixture is and a conjugated 7.

dienic monomer in solvents is an apolar solvent selected among the in which polystyrene havin weight average molecular weight comprised within range of from 30,000 to 120,000 is concentrations of from 5 to 20% by initiators are alkyl-lithium compounds originate a living polymeric system.

system can contain polar amines, and so forth), at 0.1% by weight relatively The percentage by weight of mixture to the first reaction process of the range of from of the T rom a t h e soluble at weight. The in order to The solvent compounds (such as ethers, a maximum concentration of to the solvent.

the monomers fed in step according to the present invention, is comprised within the 30 to 60% by weight, relatively to all monomers fed to the reaction. During the above disclosed reaction, a Living copolymer of Bi-T-Al type is formed.

(2) A second step, in which a percentage of the Living active centres generated during the first reaction step are quenched by means of the addition to the reaction system of compounds characterized in that they contain acidic hydrogen atoms (H20, alcohols, and so forth) in their chemical structure. The amount of active centre quenchers second step of such a process is range of from 10 to 50% by moL, of initiator fed to the first step. third step, in which a conjugated diene is fed to Living system coming from the second step and undergoes a complete conversion.

m o 1 e s (3) A t h e added to the comprised within the relatively to the 1 8.

t (1) (4) A fourth step in which a vinyLaromatic monomer is fed and is nearLy totaLLy converted.

(5) A fifth step in which the Living active centres are totaLLy quenched by feeding a compound with an acidic reactivity.

In such a way, the bLend of the two copoLymers Bi-T-Al-B2-A2 + Bi-T-Al is obtained.

This process is carried out under the above indicated generaL conditions of temperature and pressure, i.e., at temperature vaLues comprised within the range of from 300C to 1500C and under atmospheric, or superatmospheric pressure.

One of the variants constituting aLternative routes for the above said process comprises, at the end of the first step of poLymerization of the mixture of monomers, a second step in which a second aLiquot of initiator is f e d.

Such a route Leads to the formation of an additionaL number of active centres, on which pure bLock copoLymers, previousLy described by means of the formuLa B3 -T-A3 are formed.

In that case, the various sequentiaL steps are: Synthesis of a pure dienic bLock; (2) Synthesis of a pure vinyLaromatic bLock in sequence to the dienic bLock; (3) Feed of a further aLiquot of initiator, (4) Feed of a mixture constituted by a dienic monomer and a vinyLaromatic monomer. The amount of monomers fed in mixture with each other is comprised within the 9.

t - range of from 30 to 60% reLativeLy to aLL of the monomers fed to the reaction. (5) Quenching of the Living active centres by means of a compounds which contains acidic hydrogen atoms.

By means of processes anaLogous to those as hereinabove discLosed, two poLymer bLends can be respectiveLy obtained:

Bl-Aj-B2-T-A2 + Bi-Al or B1 -T-Al -B2 -A2 + B2 -A2 - The initiators preferred for the intended purpose are those beLonging to the group consisting of both Linear and branched aLkyL-Lithium compounds, and, among them, n-butyL-Lithium and sec.-butyL-Lithium.

These initiators are customariLy used in the various steps of the process in amounts comprised within the range of from 0.025 to 0.2 parts by weight per each 100 parts of monomer submitted to poLymerization.

The soLvents suitabLe for the intended purpose are the apoLar soLvents and, among them, those in which the poLyvinyLaromatic bLocks with a weight average moLecuLar weight comprised within the range of from 50,000 to 200,000 are soLubLe; among the most suitabLe of them cycLohexane and benzene can be cited.

Said soLvents can contain poLar compounds (such as ethers, amines, and so forth), whose presence aLso causes, besides an increase in the speed of reaction of poLymerization which takes in the various steps, an increase in the weight of the random copoLymeric portion T; among them, tetrahydrofuran is preferred.

The foLLowing experimentaL exampLes are iLLustrative 1 10.

is and non invention.

600 g of anhydrous cycLohexane, 55 g of (99.9% pure) styrene and 13 g of (99.85% pure) butadiene are fed to a stirred reactor of 1000 CM3; the temperature of the mass is increased up to 500C, and 0.055 g of sec.butyLLithium (in soLution in n-hexane) is fed.

minutes Later, the reaction mass reaches the temperature of 750C and the conversion of the monomers is practicaLLy compLete. Then, to the system 0. 009 g of pure methanoL and, in sequence, 7 g of butadiene are added. After 10 minutes, the reaction mass reaches the temperature of 850C and the conversion of butadiene is practicaLLy compLete.

FinaLLy, 25 g of styrene is added, and 15 minutes Later the conversion is practicaLLy compLete, with the temperature of the mass having reached the vaLue of 900C.

The quenching of the Living active centres is carried out by adding 0.5 cc of H20 to the poLymeric soLution.

1.0 g of triphenyL-nonyL-phosphite and 0.2 g of [pentaerythrityLtetraaLkyL-(3,5-di-tert.-butyL-4- hydroxyphenyL-propionate)] are added to the poLymeric soLution.

The recovery of the poLymeric bLend is carried out by means of the steam distiLLation of the reaction soLvent and subsequent drying in a vacuum oven at 600C for 24 hours.

The physicaL characteristics of the two components of the poLymeric bLend are reported in TabLe No. 1. The Limitative of the purview of the present 11 mechanical and optical properties of specimens compression-moulded at 1800C are summarized in Table No.

2.

TabLe_No._l

MW X 10-3 MW X 1()- 3 Total Block MFI (4) Example (BITA 82A2) (BiTAO styrene styrene (g/10 No. (1) (1) % (2) % (3) minutes), 1 140 80 80 68 4.5 8021y-s-i-5 GPC I.R. analysis (2) Demolition with OS04 (3) 200oC, 5 kg (4) Table-No.-2 - 850 and 12.5 2000 CM3 to 55oc Transparency % 92 Tensile strength kg/CM2 230 Elongation at break % 35 Modulus kg/CM2 8000 IZOD with notch at 230C kg x cm/cm 2.5 g2igMpj2 2 g of anhydrous cycLohexane, 37.5 g of styrene g of butadiene are fed to a stirred reactor of the temperature of the system is increased up and 0.040 g of n-butyL-Lithium (in solution in n-hexane) is fed.

minutes Later, the reaction mass reaches the temperature of 680C and the conversion of the monomers is practically complete.

Then, to the.reaction solution 0.032 g of n-butyLLithium and, in sequence, 37.5 g of butadiene are added; after 20 minutes, the reaction mass reaches the t 12.

temperature of 780C and the conversion is complete.

112.5 9 of styrene is then added to the polymeric solution and, 60 minutes later, the conversion of the monomer is complete.

The reaction is then quenched by adding 2 g of methanol to the solution containing the polymeric blend. The addition of the antioxidant, and the recovery and drying of the polymer are carried out in the same way as in Example 1.

The physical characteristics of the two components of the polymeric blend are reported in Table No. 3.

The mechanical and optical properties of specimens compression-moulded at 1800C are summarized in Table No. 4.

practically Table_No._3

Total Block MFI Example MW X 10-3 MW X 10-3 styrene styrene (g/10 No. (B I i-Al L2 -ALZ 1 SBZ-Aal---- __ % __%--- minutes) 2 170 85 75 65 3.5 TabLe_No._4 - Transparency % 86 - Tensile strength kg/CM2 165 - Elongation at break % 100 - Modulus kg/cm2 7,000 - IZOD with notch at 230C kg x cm/cm 3.2 Exaln212_3 1.2 kg of cyclohexane, 0.3 9 of tetrahydrofuran, 100 g of styrene and 45 g of butadiene are fed to a reactor of 1.5 litres of capacity; the temperature of the mass is increased up to 500C, and 0.12 9 of n-butyl- f 1 13.

t lithium (in solution in n-hexane) is fed.

minutes later, the reaction mass reaches the temperature of 800C and the conversion of the monomers is practically complete.

Then, 0.012 g of H20 and, in sequence, 15 g of butadiene are added to the system.

minutes later, the reaction mass reaches temperature of 900C and the conversion of butadiene is complete.

Finally, 40 9 of styrene is added and after 15 minutes of reaction the conversion is complete.

Before recovering the solid polymer, the living active centres are quenched by adding 2 g of isopropyl alcohol to the system.

After the addition of antioxidant as in Example the recovery of the solid polymer is.carried out by steam distillation of the solvent, and subsequent drying of the solid residue at WC for 24 hours.

The physical-chemical characteristics are reported in Table 5.

Table_No._5

Block MFI Example styrene styrene MW X 1()-3 MW X 1()-3 (g/10 No. % V __ (BIlAiBIA22 jBijA minutes) U 2 3 70 50 130 80 8.5 9M!2 4 1 ' kg of the blend disclosed in Example 3 is mixed with 5 kg of commercial crystal polystyrene EMw(GFe) = 250 x 103]. Said mass is fed to a twin- screw extruder equipped with a heated jacket. This operation is repeated i 14.

1 is twice in order to enable the optimal mixing to be obtained; the material is then transformed into granules of 0.5 cm of length.

The properties of the so prepared compound are determined on specimens compression-moulded at 1800C and are reported in Table No. 6.

Table_No._6 - MFI - Transparency - Tensile strength - Elongation at break 9110 minutes kg/CM2 ka/cm2 8.2 Modulus 12,000 - IZOD with notch kg x cm/cm 3.5 Exam2Lt_5 600 g of anhydrous cycLohexane and 30 g of (99.84% pure) butadiene are fed to a reactor of 1 Litre of capacity; the mass is heated up to 600C, and 0.09 g of sec.-butyL-Lithium is added.

minutes Later, the polymerization of butadiene is complete and the reaction temperature is of about 600C.

g of (99.9% pure) styrene is then added to the system, and the reaction is complete within a time of 20 minutes; during said time period, the reaction mass reaches the temperature of 820C.

To the reaction mass 0.058 g of initiator (n-butyLLithium) and, in sequence, a reaction mixture composed by 70 g of styrene and 30 g of butadiene are added.

The reaction takes place within a 255-minutes time and the end reaction temperature is of 1020C.

A At the end of the process, 3 9 of methyl alcohol is added to the system in order to quench the active centres.

To the polymeric solution 0.8 g of TNPP (triphenyl- nonyl-phosphite) and 0,15 9 of pentaerythrityl tetraalkyl-(3,5-di-tert.-butyl-4-hydroxyphenyL)propionate are added to the polymeric solution.

The polymer is recovered by means of the steam distillation of the solvent, and the recovered polymer is subsequently dried in a vacuum-oven at 600C for 36 hours.

The physical-chemicaL characteristics and the mechanical characteristics of the polymeric blend are reported in Tables No. 7 and 8.

Table_No. 7

Total Block MFI Example styrene styrene MW X 10-3 MW X 1C)-3 (9110 No. % % __ (B B 1&2 minutes) -.111 gz 70 56 125 75 10 Table_No._8 - Transparency % 85 - Elongation at break % 125 - Tensile strength kg/cm2 1.10 - Modulus kg/cm2 6,800 - IZOD with notch at 230C kg x cm/cm 5.0 A 1 16.

C.1-2-i-Ln-l 1. Polymeric composition comprising:

(a) from 40 to 90% by weight of a linear four alternating blocks, which can be represented by the formula B1 -T-Al -B2 -A2 or B1 -Ai -B2 -T-A2 wherein:

Al and A2 are polyvinylaromatic blocks; B1 and B2 are polydienic blocks; T is a copolymeric chain portion formed by randomly linked dienic and vinylaromatic cop.olymer of monomer units; (b) from 10 to 60 parts by weight of a Linear copolymer of two blocks, which can be represented either by the formula:

B3 -T-A3 wherein: A3 is a polyvinylaromatic block either equal to, or different from, the Al block or the A2 block; 83 is a polydienic block either equal to, or different from, to B1 block or to B2 block; T has the above seen meaning; or, alternatively, by the formula:

B3 -A3 1 v 2. Polymeric composition according to claim 1, characterized in that the linear 4-block polymer (I) or (I1) has a weight average molecular weight comprised within the range of from 50,000 to 300,000.

( I 11) T A 17 is 3. Polymeric composition according to claims 1 and 2, characterized in that the average molecular weight of the polymers identified by the formulae (III) or (IV) is comprised within the range of from 20,000 to 150,000.

4. Polymeric composition according to the preceding claims, characterized in that in said composition the total amount of vinyLaromatic mono of from 60 being constit comprised within the range with the balance to 100% monomeric units.

5. Polymeric composition according to the preceding claims, characterized in that the dienic blocks are poLybutadiene blocks and the poLyvinyLaromatic blocks are poLystyrenic blocks.

6. Polymeric composition according to the preceding claims, characterized in that the individual components are blended in order to constitute 7. Process for preparing a according to the - in a first step vinvLaromatic m e r i c u n i t s i to 90% by weight uted by dieni preceding claims, metered amounts monomer are polymer each other by Living anionic complete, or nearly complete, in a second step a percentage comprised range o f produced quenched containing a metered from the s t e p b y the same composition. polymeric composition characterized in that: of a diene and of a i zed lvmeri za in mixture with po t i o n, up to monomer conversion; from 10 to 60% of the active by the first reaction step by means of the addition acidic hydrogen atoms; amount of diene is added to the mass coming second step, and is polymerized in a third means of the Living anionic polymerization w i t h i n t h e living centres are partially of compounds 18.

1 route until the conversion of fed diene is complete or substantially complete; a metered amount of vinyLaromatic monomer is added to the product coming from the third step and is polymerized, in a fourth step, until the conversion of the vinyLaromatic monomer fed is complete or substantially complete; the blend of polymers polymerization product preliminary complete X centres by means hydrogen atoms, constituted by the B1 is recovered from the s from the fourth step, after the quenching of the living active o a compound which contains acidic in that way the polymeric blend two polymers -T-Al-B2-A2 + Bi-T-Al being obtained.

8. Process for preparing a polymeric composition according to claims from 1 to 5, characterized in that:

in a first step metered amounts of a conjugated diene are polymerized by Living anionic polymerization, up to complete, or nearly complete, monomer conversion; in a second step, a metered amount of a vinyLaromatic added to the reaction mass coming from the s polymerized until the conversion of monomer fed is complete or monomer is first step and i vinyLaromatic Ly complete; t h c substantial in a third step, the partial quenching is carried out of a percentage comprised within the range of from 10 to 60% of the active centres produced in the previous steps by means of the addition of compo.unds containing acidic hydrogen in a fourth a t 0 m S; step a mixture 1 constituted by metered a.

1 19.

amounts of a diene and of a vinyLaromatic fed, and the polymerization is continued conversion of said monomers is complete, complete; monomer is unti L t h e or nearly - the produced blend of polymer coming from the fourth step is recovered after the preliminary quenching of the living active centres by means of a compound which contains acidic hydrogen atoms, in that way the polymeric blend constituted by the polymers El-Al-B2-T-A2 4 B1-Al being obtained.

9. Process for preparing a polymeri according to claims from 1 to 5, characterized in a first step metered amounts of a conjugated are polymerized by complete, composition in that:

diene Living anionic polymerization, up to or nearly complete, monomer conversion; a second step, a metered amount of a vinyLaromatic monomer is added to the reaction mass coming from the first step and is polymerized until the conversion of the vinyLaromatic monomer fed is complete or substantially complete; a third step, a vinylaromatic in further aliquot of i anionic polymerization is added; in a fourth step metered amounts of a diene and of a monomer, in mixture with each other, and amounts comprised within the range of from 30 to 60% iveLy to the monomers fed to the process are added the poLymerization is continued untiL the compLete, compLete, conversion of the monomers is i n r e 1 a t and o r n e a r 1 y obtained; the copo lymer is n i t i a t o r o f recovered from 1 1 among the 20.

poLymerization products coming from the fourth step, after the preLiminary quenching of the Living active centres by means of the addition of a compound which contains acidic hydrogen atoms, in that way the poLymeric bLend constituted by the two poLymers Bl-Al-B2-T-A2 4' B2-T-A2 being obtained.

10. Process for preparing a poLymeric composition according to cLaims from 1 to 5, characterized in that:

in a first step metered amounts of a conjugated diene and of a vinyLaromatic monomer, in mixture with each other, are poLymerized by Living anionic poLymerization, up to compLete, or nearLy compLete, monomer conversion; in a second step, a further aLiquot of initiator of Living anionic poLymerization is added; in a third step, a metered amount of a conjugated diene is added and the poLymerization is continued untiL the conversion of the monomer is compLete or substantiaLLy compLete; - in a fourth step a metered amount of a vinyLaromatic monomer is fed and the poLymerization is continued untiL the compLete conversion of the monomer is obtained; - the mixture of poLymers produced and coming from the fourth step is recovered after the preLiminary compLete quenching of the Living active centres by means of a compound which contains acidic hydrogen atoms, in that way a poLymeric bLend constituted by the two poLymers Bl-T-Al-B2-A2 + B2-A2 being obtained.

r, 1 R c 1.

11. Process according to cLaims 7, 8, 9, 10, characterized in that the poLymerization is carried out by operating in an organic, aLiphatic or cycLoaLiphatic soLvent at temperatures comprised within the range of from 30 to 1500C and under a pressure equaL to, or higher than, atmospheric pressure, in the presence of an aLkyLmetaL or of an aryL-metaL.

12. Process according to cLaim 11, characterized in that the poLymerization can be carried out in the presence of at Least one Linear or cycLic, poLar compound seLected from among ethers or amines, in amounts comprised within the range of from 0.01 to 0.1 parts by weight, reLativeLy to the soLvent.

13. Process according to cLaims 7, 8, 9, 10, characterized in that the soLvent is cycLohexane and the reaction temperature is comprised within the range of from 50 to 1000C, the initiator is an aLkyL-Lithium containing from 3 to 7 carbon atoms in the aLkyL group, and said initiator is used in amounts comprised within the range of from 0.025 to 0.20 partsby weight per each 100 parts by weight of vinyL-aromatic monomers.

14. Process according to cLaims 7, 8, 9, 10, characterized in that the diene is butadiene and the vinyLaromatic compound is styrene.

Published 1990atThe Patent Office. State House. 66 71 High H:.aorr, LcndorWCR47F Pi.,rthercopaesmkv be obtamedfrorn The PaertOfflce Sales Branch. St Mar, Cray. Orpington. Kent BR5 3Rr PinitE- by techniques Itd. St Y.a-_v Cra,- Kcnt. Cc;z 1 87