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Title:
METHOD FOR PRODUCING DIENE-VINYLAROMATIC COPOLYMER RUBBERS MODIFIED WITH A POLAR MONOMER
Document Type and Number:
WIPO Patent Application WO/2017/116270
Kind Code:
A1
Abstract:
The invention relates to a method for producing diene-vinylaromatic copolymer rubbers modified with a polar comonomer, by emulsion copolymerization of conjugated dienes, vinylaromatic monomers, and polar comonomers in the presence of a radical initiator, a molecular-weight regulator, and an emulsifying agent, followed by the separation of a rubber from latex. In the method provided by the invention an antioxidant is added to the vinylaromatic monomer to be polymerized, in the form of a sterically hindered phenol in an amount of from 0.2 to 0.6 wt.%, and vinyl derivatives modified with polar groups of various classes are used as the modifying polar comonomer, wherein the polar monomer is added batchwise during the process: a first portion in an amount of 0.5 to 1.0 weight part is added together with hydrocarbon charge, and a second portion and a third portion are added in an amount of 0.5 to 2.5 weight part at monomer conversions of from 30 to 40 and from 50 to 60%, respectively. The method provided by the invention may be used in the synthetic rubber production and tire industry and allows for reduction of power consumption during production of rubbers having improved physical and mechanical properties in vulcanizates thereof.

Inventors:
KORYSTINA LUDMILA ANDREEVNA (RU)
ZHURIKHINA MARINA APPOLONOVNA (RU)
SUKHAREV ALEXANDER VIKTOROVICH (RU)
MAXIMOV DENIS ALEXANDROVICH (RU)
RAKHMATULLIN ARTUR IGOREVICH (RU)
Application Number:
PCT/RU2015/000961
Publication Date:
July 06, 2017
Filing Date:
December 30, 2015
Export Citation:
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Assignee:
SIBUR HOLDING PUBLIC JOINT STOCK CO (RU)
International Classes:
C08F236/10; C08F2/44; C08L9/06
Foreign References:
RU2115664C11998-07-20
US20110269930A12011-11-03
RU2101300C11998-01-10
RU2064925C11996-08-10
US20110098404A12011-04-28
Attorney, Agent or Firm:
LAW FIRM "GORODISSKY & PARTNERS" LTD (RU)
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Claims:
CLAIMS

1. A method for producing diene-vinylaromatic copolymer rubbers modified with a polar comonomer, by emulsion copolymerization of conjugated dienes, vinylaromatic monomers, and polar comonomers in the presence of a radical initiator, a molecular-weight regulator, and an emulsifying agent, followed by the separation of a rubber from latex, characterized in that a sterically hindered phenol as an antioxidant is added to the vinylaromatic monomer to be polymerized, in an amount of from 0.2 to 0.6 wt.%, and vinyl derivatives modified with polar groups are used as the modifying polar comonomer, wherein the polar monomer is added batchwise during the process: a first portion in an amount of 0.5 to 1.0 weight part is added together with hydrocarbon charge, while a second portion and a third portion are added in an amount of 0.5 to 2.5 weight part at monomer conversions of from 30 to 40 and from 50 to 60%, respectively.

2. The method according to claim 1 , wherein 1 ,3 -butadiene, isoprene, 1,3- ethylbutadiene, 1 ,3-pentadiene, 1,3-hexadiene, 1 ,3-cyclooctadiene, 1 ,3-octadiene, or a mixture of any of said compounds is used as the conjugated dienes.

3. The method according to claim 1 , wherein the conjugated dienes are 1,3- butadiene.

4. The method according to claim 1, wherein the vinylaromatic monomer is styrene, a-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-cyclohexylstyrene, para- chlorostyrene, 1 -vinylnaphthalene, 2-vinylnaphthalene, or a mixture thereof.

5. The method according to claim 1, wherein the vinylaromatic monomer is styrene or a-methylstyrene.

6. The method according to claim 1 , wherein the polar comonomer is a vinyl derivative comprising polar groups.

7. The method according to claim 6, wherein the polar comonomer is modified with polar groups selected from ester, carboxyl, amide, nitrile groups and heterocyclic groups containing pyridine ring.

8. The method according to claim 6, wherein the polar groups are selected from the group comprising: ether groups, hydroxyester groups, oxyrane ring-containing ester groups, and pyridine groups.

9. The method according to claim 6, wherein the vinyl derivatives modified with polar groups are (hydroxy)alkylmethacrylates of general formula:

wherein R is Ci-C4alkyl or hydroxy-Ci-C4alkyl.

10. The method according to claim 1 , wherein the antioxidant is a substituted phenol f the following formula:

wherein Ri is Ci-C4alkyl,

n is 1 , 2, 3, or 4;

X is -CH2-, -CH2-CH2-C(0)-0-CH2-, or -CH2-C(0)-CH2-CH2-; and

if n is 1, 2, or 3, X is -CH2-, -CH2-CH2-C(0)-0-CH2-,

if n is 4, X is -CH2-CH2-C(0)-, and

R2 is C4-Cig when n is 1 ;

R2 is -CH2- when n is 2; and,

R2 is =CH- when n is 3; and,

R2 is =C= when n is 4; or

when n is i, then -X-R2 represents Ri .

1 1. The method according to claim 1, wherein the antioxidant is selected from the group including: Irganox 1010 (pentaeritrite-tetrakis-[3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate), Irganox 1076 (octadecyl-3(3,5-di-tert-butyl-4- hydroxyphenyl)propionate), Irganox 1520 (2,4-bis-[(octylthio)methyl]-ortho-cresol), Irganox 245 (triethyleneglycol-bis(3-tert-butyl-hydroxy-methylphenyl)propionate), 2,6- di-tert-butyl-4-methylphenyl, 2,4,6-tri-tert-butylphenol, 2,6-di-tert-butyl-para-cresol, 2,6-bis-(l,l-dimethylethyl)-4-methylphenol, octadecyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate, and 3,5-bis(l,l-dimethylethyl)-4-hydroxyphenyl-C13- Ci5alkyl ester of benzenepropionic acid.

12. The method according to claim 1, wherein the copolymer emulsion is filled with an aromatic oil-softening agent before separation at the weight ratio of polymenoil of (72-75):(28-25).

13. A copolymer of conjugated diene, a vinylaromatic monomer, and a polar comonomer produced by the method according to any one of claims 1 to 12.

14. The copolymer according to claim 13, wherein the conjugated diene is butadiene- 1,3, the vinylaromatic monomer is (methyl)styrene, and the polar comonomer is (hydroxy)alkylmethacrylate.

Description:
METHOD FOR PRODUCING DIENE-VINYLAROMATIC

COPOLYMER RUBBERS MODIFIED WITH A POLAR MONOMER

The present invention relates to the field of production of functionalized diene- vinylaromatic copolymer rubbers, preferably butadiene-styrene rubbers, by emulsion copolymerization of conjugated dienes with vinylaromatic monomers in the presence of a polar comonomer.

Butadiene-styrene rubbers (SKS) produced by emulsion polymerization are widely used in various fields of industrial production. Especially high levels of SKS are used in the tire industry, which is a result of rather high performance characteristics of vulcanized rubbers produced on their basis and a lower prime cost compared to solution polymers. Recently, special attention is paid to increasing the wear resistance and optimization of elastic-hysteresis properties of automobile tires. These properties are achieved by addition of small amounts of - monomers containing functional groups to the polymerization process . The monomers may be acrylic monomers, such as methacrylic acid, nitrile acrylic acid, methacrylic acid methyl ester, methacrylic acid 2- hydroxyethyl ester, methacrylic acid 2-hydroxyethylamide, etc. Copolymers with monomers comprising hydroxyl and amide groups have the best properties.

Emulsion butadiene-styrene rubbers (EBSR) are known to be produced by polymerization of butadiene and styrene in an aqueous solution of an emulsifying agent, wherein the initiation is performed using a redox system. In order to prevent the formation of a cross-linked or branched polymer, the process is carried out until the conversionof monomers reaches 60-70% (Kirpichnikov P.A., Averko-Antonovich L.A., Averko-Antonovich Yu.O., Khimiya i tekhnologiya sinteticheskogo kauchyuka [Chemistry and Technology of Synthetic Rubber], "Khimiya", 1970, p.416).

The destruction of a polymer initiated by oxygen and accelerated by relatively high temperatures and mechanical impacts during separation process is prevented by addition of stabilizing antioxidants to the latex in the form of dispersions, emulsions, or solutions in oils. Antioxidants that have gained a wide use are antioxidants on the basis of sterically hindered phenols of general formula (Erkova L.N., Chechik O.S., Latexes; L.:Khimiya, 1993, p.94):

wherein i is C 1 -C 4 alkyl;

n is 1 , 2, 3, or 4;

X is -CH 2 -, -CH 2 -CH 2 -C(0)-0-CH 2 -, or -CH 2 -C(0)-CH 2 -CH 2 -; and

if n is 1 , 2, or 3, X is -CH 2 - or -CH 2 -CH 2 -C(0)-0-CH 2 -,

if n is 4, X is -CH 2 -CH 2 -C(0)-CH 2 -;

R 2 is C 4 -Ci 8 if n is 1 ;

R 2 is -CH 2 - if n is 2;

R 2 is =CH- if n is 3; and

R 2 is -C= if n is 4; or

if n is 1, X-R 2 may represent R \ .

RU 232851 1 discloses a process for producing butadiene-styrene rubbers by radical copolymerization in an emulsion solution of at least one conjugated diene monomer with a comonomer-precursor which is hydrolyzable or oxidizable to a carboxylic acid. The intermediate diene elastomer produced thereby comprises functional groups along the chain, said groups being converted into carboxylic groups after hydrolysis or oxidation. The comonomer can belong to the group of compounds including alkyl acrylates and alkyl methacrylates. Co-polymers according to the discussed patent can comprise 20 to 99 wt.% diene monomers and 1 to 80 wt.% vinylaromatic compounds. The method provides butadiene-styrene polymers functionalized with alkyl acrylates and alkyl methacrylates, including oil-filled ones. However, this method is difficult to carry out. In addition, latex is stabilized by a mixture of antioxidants AO 2246 and S13 (80%:20%) in an amount of 1 wt.% based on elastomer, which implies an additional step of preparing an antioxidant dispersion that is introduced into the latex mixture before separation.

In another known method for producing emulsion butadiene-styrene rubbers modified with a polar monomer (RU 2064925), said polar monomer is nitrile acrylic acid (NAA) in the weight ratio of butadiene :styrene:NAA being (66-91):(8-25):(l-9), wherein NAC is added batchwise during the polymerization. The obtained rubber is characterized by high dynamic fatigue strength, low durability (185-210), and high resistance to heat aging. However, NAA is a highly toxic compound that is hazardous to human and environment.

There is known a method for producing functionalized butadiene-styrene copolymers (US201 1098404) by emulsion copolymerization of butadiene, styrene, and an epoxyacrylate monomer. The monomer ratio of butadiene: styrene :epoxyacrylate is (45-85):(10-50):(0.1 -10) weight parts, and the polymerization is performed at temperature of 0-70°C (optimally at 10°C) for 4-48 hours (optimally for 24 hours). Vulcanized rubbers produced from such polymer are characterized by improved wear resistance and dynamic and elastic-hysteresis characteristics. However, epoxyacrylate can cause premature uncontrolled crosslinking of the polymer during monomer recovery.

Further, another method of copolymerization of butadiene, styrene, and a modified hydrophilic chain-transfer agent provides a polymer with terminal functionalized groups (US2013289200). The hydrophilic chain-transfer agent is produced by polymerization of acrylate monomers in an inert hydrocarbon solvent (carbon tetrachloride) in the presence of a free-radical initiator. Emulsion polymerization is conducted at temperature between 0 and 70°C for 4-48 hours. However, the use of carbon tetrachloride to produce emulsion rubbers is not advisable due to its significant toxicity and ability to slow down processes of vulcanization of a rubber mixture.

There is also known a method for producing butadiene-styrene rubber by emulsion copolymerization (US 6512053) of butadiene, styrene, and hydroxyalkyl acrylate. According to this technical solution, a functionalized butadiene-styrene rubber is produced by synthesis of a high molecular-weight butadiene-styrene polymerizate and a low molecular-weight butadiene-styrene polymerizate by a free-radical emulsion polymerization, which significantly complicates the method for producing the functionalized butadiene-styrene rubber.

In another known method (US 2012165462), a functionalized butadiene-styrene copolymer is produced by emulsion copolymerization of butadiene, styrene, and a reactive, high molecular-weight monomer (preferably polypropylene glycol or polyalkylene glycol) at a ratio of (45-85):(10-50):(0.1-10) wt.%.

Said copolymer has a high affinity for silica, improved wet grip, and high abrasion resistance. A drawback of the discussed invention is a high cost of the proposed modifier.

An introduction of functional groups into the composition of emulsion butadiene-styrene rubber provides significantly improved characteristics of vulcanized rubbers produced on their basis. However, the polymerization up to a standard conversionof monomers (about 70%) results in that the obtained latex comprises a significant amount of non-polymerized monomers which are removed at the step of degasing the latex, then purified, and recycled (to prepare hydrocarbon charge). The process of the purification of recycled butadiene is cost demanding and leads to an increase in the cost of emulsion rubbers.

There is known a method for producing emulsion butadiene-styrene rubbers (WO2010083089) which provides the conversionof monomers increased to 95% resulted from the polymerization carried out in the presence of a sufficient amount of an antioxidant (substituted phenol) added at the step of synthesizing latex, wherein the formulation and parameters of the process do not differ from the standard ones. In addition, it has been found that if the antioxidant doses are more than 0.2 wt.%, further addition of a stabilizer into the latex to separate rubber is not required, and the rubber produced by this method do not comprise gel at an increased conversionof monomers.

However, the execution of the process up to such high conversion requires significantly increased doses of an emulsifying agent after reaching a conversion of 60- 70% to prevent destabilization of the system.

The closest prior art to the present invention is a method for producing butadiene-styrene (oc-methylstyrene) rubbers modified with a polar monomer, wherein the polar monomer is alkyl methacrylate, and alkali soap of tallow oil or a mixture of alkali soaps and resinous and fatty acids are used as an emulsifying agent (RU 21 15664). The copolymerization is carried out at the following ratio of monomers, wt.%: butadiene, 50-88; styrene or a-methylstyrene, 10-40; and alkyl methacrylate, 2- 10. After recovering unpolymerized monomers with aqueous vapor, the latex is filled with a mixture of antioxidants, in particular agidol-2 and diafen FP, and coagulated with a solution of sodium chloride and sulfuric acid. However, this method does not provide the conversion of monomers of more than 70% and requires an additional step of adding a mixture of antioxidants before separation.

The technical objective to be addressed by the present invention is to increase the conversion of monomers up to 85%, simplify the method, and reduce the power consumption during the production of rubber, as well as vulcanized rubbers with improved physical and mechanical characteristics produced therefrom.

The posed objective is addressed by a proposed method for producing functionalized diene-vinylaromatic copolymer rubbers by emulsion copolymerization of conjugated dienes with vinylaromatic monomers and a polar comonomer in the presence of a radical initiator, a molecular weight regulator, and an emulsifying agent, followed by separation of the obtained rubber from the latex. In addition, the claimed method is characterized by that during the production of said modified diene- vinylaromatic copolymer, an antioxidant is added to a vinylaromatic monomer to be polymerized, the antioxidant being in the form of sterically hindered phenols in an amount of 0.2 to 0.6 wt.%, and the used modifying polar comonomer is a vinyl derivative modified with polar groups of different classes, wherein the polar monomer is added batchwise during the process: a first portion is added together with hydrocarbon charge in an amount of 0.5 to 1.0 wt.%, while a second and a third portion is added in an amount of 0.5 to 2.5 wt.% at the conversionof monomers being 30-40% and 50-60%, respectively.

The present invention also relates to a copolymer of conjugated diene with a vinylaromatic monomer and a polar comonomer produced by the above-indicated method.

The invention allows facilitation of the method of emulsion copolymerization of diene-vinylaromatic rubbers by exclusion of the step of preparing an antioxidant emulsion from the technology process, reduction of power consumption by an increase in the conversion of monomers, and an increase of the quality of rubber due to reduced gelation in a polymer.

Hereinafter, the present invention is described in more details, in particular, with references to examples of embodying thereof.

The invention relates to the method for producing diene-vinylaromatic copolymer rubbers modified with a polar comonomer by water-emulsion copolymerization of conjugated dienes, vinyl-substituted aromatic monomers and polar comonomers.

The conjugated diene can be 1,3 -butadiene, isoprene, 1,3-ethylbutadiene, 1,3- pentadiene, 1 ,3-hexadiene, 1,3-cyclooctadiene, 1,3-octadiene or a mixture thereof.

It is more preferable to use 1,3-butadiene.

The vinylaromatic monomer can be styrene, oc-methylstyrene, para- and meta- isomers of vinyltoluene (3-methylstyrene, 4-methylstyrene), 4-cyclohexylstyrene, para- chlorostyrene, 1 -vinylnaphthalene, 2-vinylnaphthalene, and a mixture thereof.

Styrene and -methyl styrene are most preferable as the vinylaromatic monomers.

In the present invention, styrene and -methylstyrene can be also denoted by the general term "(methyl)styrene".

As the polar comonomers, vinyl derivatives can be used which have been modified with polar groups of various classes, including the groups such as ester, carboxyl, amide, nitrile, heterocyclic groups, etc. Vinyl derivatives comprising, as the polar groups, both ether groups, hydroxyester groups, oxyrane ring-containing ester groups, and heterocyclic groups, in particular heterocyclic groups containing pyridine cycle, are preferable, especially pyridine groups.

The polar monomer can be, in particular, acrylic acid ester, methacrylic acid ester, glycidyl methacrylate, hydroxyethyl methacrylate, ethylhexyl methacrylate, an acid such as methacrylic, fumaric, or itaconic acid, vinylpyridine, or 2-methyl-5- vinylpyridine, etc.

The most preferable polar monomer is (hydroxy)alkyl methacrylate of general formula:

wherein R is Ci-C 4 alkyl or hydroxy-Ci-C4alkyl.

The copolymerization according to the present invention is carried out at the following monomer ratio, wt.%: conjugated diene, 68-65%; vinylaromatic monomer, 28-32%; and polar comonomer, 2-5%. The polar monomer is added batchwise during the process, as follows: 0.5-1.0 weight part with hydrocarbon charge and 0.5-2.5 weight parts when the conversion of monomers reaches 30-40% and 50-60%.

The batchwise addition of the polar monomer improves the compositional heterogeneity of the produced copolymers.

The process of copolymerization according to the present invention comprises adding an antioxidant to monomer charge.

The antioxidant is a sterically hindered phenol, preferably a substituted phenol of the following formula:

wherein Ri is Ci-C 4 alkyl,

n is 1, 2, 3, or 4;

X is -CH 2 -, -CH 2 -CH 2 -C(0)-0-CH 2 -, or -CH 2 -C(0)-CH 2 -CH 2 -; and

if n is 1 , 2, or 3, X is -CH 2 -, -CH 2 -CH 2 -C(0)-0-CH 2 -;

if n is 4, X is -CH 2 -CH 2 -C(0)-CH 2 -;

R 2 is C 4 -C i8 if n is 1 ;

R 2 is -CH 2 - if n is 2;

R 2 is =CH- if n is 3; and

R 2 is =C= if n is 4; or

when n is i , then -X-R 2 may represent Ri .

In particular, the following antioxidants can be used as such a compound: ganox 1010 (pentaerytrite-tetrakis-[3-(3,5-di-tert-butyl-4-hydroxypheny l)propionate):

Irganox 1076 (octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), Irganox 1520 (2,4-bis-[(octylthio)methyl]-ortho-cresol), Irganox 245 (triethylene glycol-bis(3-tert-butyl-hydroxy-methylphenyl)propionate), Ionol (2,6-di-tert-butyl-4- methylphenol), P-23 (2,4,6-tri-tert-butylphenol).

In another preferred embodiment of the invention, the used antioxidant is a sterically hindered phenol that also belongs to the phenols of the above formula and is selected from the group consisting of 2,6-di-tert-butyl-para-cresol, 2,6-bis-(l,l- dimethylethyl)-4-methylphenol, octadecyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate, and 3 ,5-bis-( 1 , 1 -dimethylethyl)-4-hydroxyphenyl-C 13-C 15- alkyl ester of benzenepropionic acid.

The antioxidant is added in an amount of 0.2 to 0.6 weight part based on 100 weight parts of monomers, wherein the antioxidant is added together with the styrene at the beginning of the process, which provides an increased conversion and improved physical and mechanical properties of the polymers.

In one embodiment of the invention, the process of preparing oil-filled rubbers comprises adding an aromatic oil as a softening agent to the emulsion of a polymer (rubber), before its separation, at the weight ratio of polymenoil of (72-75):(28-25). The rubber can comprise up to 30 wt.% of an oil that is usually used for a broad spectrum of elastomers and can be added both during the separation of the rubber from the latex and during the preparation of a vulcanized rubber. The oil can be an aromatic, naphthenic, or plant oil with a low content of polycyclic compounds, such as MES (mild extract solvate) being a mild extraction raffinate, TDAE (Treated Distillate Aromatic Extracts) being a purified residual aromatic extracts, RAE (residual aromatic extracts) being a residual aromatic extract of oil selective purification, and a heavy naphthenic oil NAP (nahthenic oil product).

The elastomer according to the present invention can be synthesized by both batchwise and continuous emulsion copolymerization, in essence, by methods and under conditions known to a person skilled in the art. The reaction mixture comprises water, one or more diene monomers, one or more vinylaromatic monomers (for example, (methyl)styrene), a polar comonomer, in particular (hydroxy)alkylmethacrylate, and an acceptable initiator and an emulsifying agent.

The polymerization can be carried out over a broad range of temperature, for example, from 5 to 50°C, more preferably between 5 and 10°C.

The emulsifying agent can be added before polymerization, as well as continuously with monomers or batchwise during the process. The emulsifying agent can be an anionic, cationic, or non-ionic surfactant. The synthesized latex can be coagulated by using acids and electrolytes, for example, sulfuric acid with polyvalent metal salts. Used acids can have the pH of lower than 4; however, they should be used carefully since a strongly acidic medium allows hydrolysis of ester groups. Useful anticoagulants are cationic polyelectrolytes based on ammonium salts. According to the present invention, the polymer can be selected, for example, by using a mixture of sulfuric acid with a cation-active polyelectrolyte based on polydiallyldimethylammonium chloride (polyDADMAC).

The choice of the polymerization initiator depends, in particular, on the type of the used polymerization, which can be cold or hot polymerization.

Cold polymerization is characterized by that it runs at temperature of from 5 to 8°C.

The used initiator is, as a rule, a redox system of a chelate complex of iron and organic hydroperoxide with rongalite used as a reducing agent (see reactions).

The mechanism of action of the redox initiating system under the cold- polymerization conditions is represented by equations (1 and 2):

Fe +2 + 2EDTA + ROOH = Fe +3 + 3EDTA + RO* + OH " (1)

Fe +3 EDTA + SFS = Fe +2 + 2EDTA (2),

wherein EDTA is ethylenediaminetetraacetic acid that forms a chelate complex with iron cations;

SFS is sodium formaldehyde sulfoxylate, rongalite.

In the case of hot polymerization, the latter is carried out by using an initiator, such as potassium or ammonium sulfate, at temperature of higher than 30°C. The initiator degrades into free ion-radicals according to the following scheme:

K 2 S 2 0 8 = 2K + +2*S0 4 "2 .

Mercaptan is added to control the chain length and molecular-weight distribution. The thiol group of mercaptan acts as a chain transfer agent to prevent achieving high molecular weights which are possible in emulsion systems. The S-H bond in the thiol group is able to attack the growing polymer radical resulting in extraction of a hydrogen atom. The scheme of the action of the molecular-weight regulator is shown in equations (3 and 4), wherein RS* initiates the growth of a new chain. Thiol also prevents the gel formation and improves the processability of elastomer, providing its linearity.

P* + RSH = PH + RS* (3)

RS* + M = RSM* (4),

wherein P* is a growing polymer radical;

RSH is mercaptan, and M is a monomer molecule.

In the case of hot polymerization, the initiator can be, in one embodiment, for example, potassium persulfate.

The parameters of the reaction system, such as temperature, reaction rate, and stirring are under control until the conversion reaches required values. Polymerization, as usual, runs to the conversion of 60% in cold polymerization and 70% in hot polymerization, then a stopper is added to terminate the radical polymerization. The used stopper is, in general, diethylhydroxylamine or sodium dimethyldithiocarbamate, or a mixture thereof.

Variants of the invention embodiment are illustrated in the following examples which must not limit the present invention.

Table 1 shows the components of the polymerization systems used in the examples which include monomers involved in the reaction in the form of emulsion with emulsifying agents and an initiating system.

Example 1 (comparative, according to prototype RU 21 15664)

Copolymerization of butadiene, styrene, and methyl methacrylate was carried out according to the formulation given in Table 1. Sodium soap of non-disproportionate tallow oil was used as an emulsifying agent. Copolymerization was carried out in a 60- liter autoclave equipped with a mixer and a jacket cooling at temperature 5-8°C. The autoclave was filled with a water phase consisting of the emulsifying agent, leukanol, trisodium phosphate, rongalite, an iron-trilon complex, and softened water. Further, calculated amounts of styrene and methyl methacrylate, a regulator (tertiary dodecyl mercaptan), and butadiene were added. The monomer ratio of butadiene: styrene: methyl methacrylate in weight percentage was 72:20:8. Pinane hydroperoxide was dosed at temperature 5-6°C. When the conversion reached 65-70 wt.%, the polymerization process was terminated by a 1 % solution of sodium dimethyldithiocarbamate added to the autoclave.

Non-polymerized monomers were selected from the latex by water-steam distillation under vacuum. The latex, after filling with a suspension of an antioxidant mixture of sterically hindered phenols, such as Agidol-2 (2,2'-methylene-0/5-(4-methyl- 6-tert-butylphenol)) and diafen FP (N-phenyl-N'-isopropyl-n-phenylenediamine), was coagulated with a solution of sodium chloride and sulfuric acid at temperature of 30- 40°C, and the pH of the dispersion medium (serum), i.e. aqueous medium where the polymer was in a dispersion phase, was from 4 to 6. The rubber was washed with water 3-4 times at 40-60°C to remove impurities, pressed in a roller washing machine to reach a residual moister of 5-15 wt.%, and dried at temperature of 80-120°C.

The rubber was analyzed on the amount of bound styrene and methyl methacrylate by NMR-spectroscopy.

The amount of gel in the polymer was determined based on the weight of a dry residue, m, remained on the filter screen after filtration of the dissolved polymer weighing 7.9 g in 175 cm toluene. According to the method, the process of dissolution ran for 4-24 hours at 25±10°C. Then, the solution was filtered by passing through a metal screen, and the screen was dried to a constant weight at 70°C. The content of gel in the polymer was calculated as an m/M ratio expressed in percentage.

A rubber mixture was prepared according to the formulation given in Table 2 to obtain copolymer vulcanizates. Vulcanization was performed at temperature of 142±1°C for 40 minutes. Physical and mechanical, and dynamic properties of the rubber was determined based on GOST 270-75, 265-66, and 161 -79, wear resistance was determined as a value of a wear volume loss based on GOST 12251-77, and resistance to heat-aging was determined based on GOST 9.024-74. The results are given in Table 3. The results of the determination of physical and mechanical properties and the amount of gel are given in Table 3.

Example 2

Copolymerization of butadiene, styrene, and methyl methacrylate was carried out in the same way as in Example 1 with a difference consisting in that the mixture of potassium soaps of non-disproportionate colophony and natural fatty acids in a ratio of 50:50 was used as an emulsifying agent, sodium carbonate was used as an electrolyte, and methyl methacrylate was added batchwise in an amount of 2 weight parts at three points: 0.5 weight part was added together with styrene at the beginning of the process, 0.5 weight part was added at the conversion of 35%, and 0.1 weight part was added at the conversion of 55%. Antioxidant Irganox 1520L was added in a styrene solution at the beginning of the polymerization. The polymerization process was carried out until the conversion reached 82%, and the separation was performed by salt-free coagulation (coagulating mixture comprised Superfloc C-592 and sulfuric acid) without adding an antioxidant suspension. The temperature during the separation was 50-60°C, the pH of serum was 4-6, and the washing and drying conditions were the same as in Example 1.

The rubber was analyzed on the amount of bound styrene and methyl methacrylate by NMR-spectroscopy.

A rubber mixture was prepared according to the formulation in Table 2 to obtain copolymer vulcanizates. Vulcanization was performed at temperature of 142±1°C for 40 minutes.

Physical and mechanical properties were determined based on GOST 270-75,

265-66, and 161-79, wear resistance was determined based on GOST 12251-77, and the amount of gel in the polymer was determined based on the weight of a dry residue, m, remained on the filter screen after filtration of the dissolved polymer weighing 7.9 g in 175 cm 3 toluene. The process of dissolution ran for 4-24 hours at 25±10°C. Then, the solution was filtered by passing through a metal screen, and the screen was dried to a constant weight at 70°C. The content of gel in the polymer was calculated as an m/M ratio expressed in percentage.

The results of the determination of physical and mechanical properties and the amount of gel are given in Table 3.

Example 3

Copolymerization of butadiene, styrene, and methyl methacrylate was carried in the same way as in Example 2 with a difference consisting in that the total dose of methyl methacrylate was 4 weight parts, and it was added batchwise at three points: 1.0 weight part was added together with styrene at the beginning of the process, 1.5 weight parts were added at the conversion of 35%, and 1.5 weight parts were added at the conversion of 55%, wherein the conversion of monomers was 82%.

Vulcanizate of the rubber copolymer obtained in Example 3 was prepared in the same way as in Example 2. Physical and mechanical properties of the obtained vulcanizates and the content of gel were determined by methods described in Example 2. The results are given in Table 3.

EXAMPLES 4 to 1 1

Samples according to examples 4-10 were synthesized in the same way as in

Examples 2 and 3 with a difference consisting in that the doses of (hydroxy)alkyl methacrylate and an antioxidant corresponded to those given in Table 1, and in Examples 9, 10, and 13 styrene was replaced with methylstyrene.

Samples according to example 1 1 were synthesized in the same way as in Examples 2-10 with a difference consisting in that the doses of all components corresponded to those given in Table 1 , and during the separation, the rubber was filled with aromatic oil Norman 346.

Vulcanizates of the rubber copolymers obtained in Examples 4-1 1 were prepared in the same way as in Example 2. Physical and mechanical properties of the obtained vulcanizates were determined by the methods described in Example 2. The results are given in Table 3.

Examples 12-13 (comparative)

Samples of examples 12 and 13 were synthesized in the same way as in Example 1 with a difference consisting in that a modifying monomer was not used, the latex was filled with an antioxidant during the separation, and the doses of all components corresponded to those given in Table 1. During the separation, the rubber of example 12 was filled with an emulsion of antioxidant VS-30 A, and the rubber of Example 13 was filled with aromatic oil Norman 346 admixed with antioxidant VS-1 (examples 12-13 are comparative).

Vulcanizates of the rubber copolymers obtained in Examples 12-13 were prepared in the same way as in Example 2. Physical and mechanical properties of the obtained vulcanizates were determined by the methods described in Example 2. The results are given in Table 3.

Doses of all components of the formulations according to the examples are given in Table 1. Table 1. Formulations for synthesis of rubber latexes and the order of addition of modifying monomers

Table 2. Formulation of a rubber mixture

Table 3. Properties of modified butadiene-(methyl)styrene rubber produced by the claimed method and according to the comparative examples

As seen from the data given in the tables, the claimed method for producing diene-vinylaromatic copolymer rubbers modified with a polar comonomer provides an increased conversion of monomers without deterioration of the polymer properties (the absence of branches and gel in the polymer). In addition, there are observed an increased strength properties of vulcanizates (without a reduction in a tensile strain) produced from the above-indicated modified butadiene-(methyl)styrene rubbers and a reduced wear volume loss. The method according to the present invention reduces the amount of residual recycled monomers and, therefore, power consumption for their processing and increases the yield of the target product, while providing an increased conversion of monomers.