CA1056994A - Styrene acrylonitrile copolymers with high dimensional stability under heat - Google Patents

Abstract

STYRENE ACRYLONITRILE COPOLYMERS WITH HIGH DIMENSIONAL STABILITY
UNDER HEAT

Abstract of the Disclosure Process for the production of styrene (meth)acrylo-nitrile copolymers with improved dimensional stability under heat in a homogeneous or heterogeneous phase, wherein a mix-ture of (meth)acrylonitrile and styrene containing a radical forming agent is polymerised in the presence of at least one aliphatic monoolefin with 2 - 18 carbon atoms.

Description

This invention relates to thermoplastic moulding compounds with high dimensional stability under heat and soft flow which are produced by the copolymerisation of styrene and acrylonitrile in the presence of aliphatic monoolefins.
It has long been known that styrene-acrylonitrile copolymers have a better dimensional stability under heat than poly-styrene (see United States patent specification 2,102,179 issued December 14, 1937 to I.G. Farben-industrie AG). Several patents describe the synthesis of the copolymers (see United States patent specifications 2,140,048 issued December 13, 1938 to I.G. Farbenindustrie AG; 2,439,202 issued April 6, 1948 to United States Rubber Company and German patent specifications 961,309 issued April 4, 1957 to Badische Anilin- ~ Soda-Fabrik AG; 1,003,446 issued August 14, 1957 to Badische Anilin- ~ Soda-Fabrik AG), and improvements in the methods for achieving special product qualities (see United States patent specification ~; 3,772,257 igsued November 13, 1973 to Knapsack AG = German Offenlegungsæchrift

2,057,250 and United States patent specification 3,738,972 issued June 12, 1973 to Daicel Ltd = German Offenlegungsscrift 2,142,617). According to United States Patent 2,439,202, the softening points of the copolymers rise with increasing acrylonitrile content from about 90C to 108C. According to German Patents 961,309 and 1,003,446, styrene acrylonitrile copolymers are prepared in an alcoholic suspension which have an acrylonitrile content of 28.5% and a softening point of 102C when the K-value (see H. Fikentscher, Cellulosechemie 13 (1932)) is 76, or an acrylonitrile content of 19.7% and softening point of 103C when the K-value is 84.
But styrene-acrylonitrile (SAN) copolymers which would have a high - dimensional stability under heat and very soft flow when worked up thermo-plastically without any loss in the mechanical strength properties (e.g. flex-: ural strength) of the polymers have not yet been known. Surprisingly these polymers were obtained by using aliphatic monoolefins as molecular weight regulators in the polymerisation of styrene-acrylonitrile mixtures.
This invention therefore relates to a process for the production of copolymers of styrene and (meth) acrylonitrile with ~o56994 improved dimensional stability under heat in the presence of a radical forming agent in a homogeneous or heterogeneous phase, wherein the mixtures of (meth)acrylonitrile and styrene are polymerised in the presence of at least one aliphatic monoolefin containing 2 to 18 carbon atoms, the a unt of aliphatic monoolefin present being such that in the styrene (meth) acrylonitrile copolymer obtained the aliphatic monoolefin content is from 0.1 to 1.9% by weight, based upon the weight of styrene, (meth)acrylonitrile and aliphatic monoolefin.
This invention also relates to copolymers containing a) 5 - 85% by weight, preferably 10 - 40% by weight of (meth)acrylonitrile, b) 14.99 - 93.1% by weight, preferably 89.99 - 58.1% by weight of styrene and c) 0.01 - 1.9% by weight of an aliphatic monoolefin, the sum of a ~ b ~ c being 100%.
- The polymers produced by the process according to the invention have intrinsic viscosities of 0.5 to 10 (dl/g) Cdetermined from a solution `~ in dimethylformamide at 25C7. The molecular weights determined by the method of light scattering are between 40,000 and 5,000,000. The non-unifor-mity U defined by N- ~ 1, preferably lies in the range of 0.2 to 5, more , :, , preferably 1.5 to 3.5. The polymers have a random structure. The melt index values according to DIN 53 735 are between 20 and 280 rg/10 min,7 at 240C under a load of 10 kp.
Aliphatic noolefins have important advantages over the mercaptans such as dodecylmercaptan (see United States Patent No. 3,772,257) or alkyl-mercaptan mixtures (see German Published Patent Application No. 1,802,089, published May 14, 1969 in the name of Uniroyal Incorporated) which are generally used as molecular weight regulators. For example, the low boillng aliphatic olefins can easily be removed from the reaction mixtures without producing any odour which is always a problem when working with mercaptans.
Since monoolefins have a much lower tendency to transfer reactions than the sulphur derivatives, they can be used in much smaller quantities than mer-~.~

.: :

105~994 capt ~ under identical conditions. A single do~e of monoolefin at the beginning of the reaction is sufficient to ensure a con-sistent regulating action and a considerably increase of the molecular uniformity of the copolymers. It i8 surprisingly found that the addition of the monoolefins considerably improves not only the flow but also the dimensional stability under heat com-pared with these properties in polymers which have not been re-gulated.
e aliphatic monoolefins with 2 - 18 and more preferably 2 - 4 carbon atoms which may be used as molecular weight regu-. ~ . .
lators include ethylene, propylene, butene-1, butene-2, isobu-, tylene, straight chain or branched pentenes, hexenes, octenes.
, ~
Propylene and isobutylene are preferred.
Per compounds or azo compounds which split into radicals may be used as polymerisation catalysts, for example aliphatic azo dicarboxylic acid derivatives such as azobisisobutyric acid nitrile, azodicarbonamide or azodicarboxylic acid esters, per-oxides such as lauroyl peroxide, succinyl peroxide, dibenzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, j 20 ketone peroxides such as methyl ethyl ketone peroxide;
methyl isobutyl ketone peroxide; cyclohexanone peroxide;
I acetylacetone peroxide; alkyl esters of per acids such as - tert.-butyl perpivalate; tert.-butylperoctoate; tert.-butyl perbenzoate; tert.-butylperisononanate; monotertiary butyl permaleate or tert.-butalperacetate; percarbonates such as dicyclohexylpercarbonate; dialkylperoxides such as ! di-tert.-butylperoxide; dicumylperoxide; hydroperoxides such as cumene hydroperoxide; tert.-butylhydroperoxide;
peracids such as isophthalic mono-peracid or special . ~ . .

Le A 15 422 -3 -lOS6994 peroxide~ such as acetal cyclohexane sulphonyl peroxide.
Peroxides and radical starters produced in situ may l of course also be used. Suitable reactions ~or this .3 purpose are, for example, the reaction oi phosgene, ~¦ 5 chloroformic acid esters, acid halides~ isocyanates or ;j diisocyanates with hydrogen peroxide or hydroperoxides.
Pinacols or hydroperoxidised polymer substrates may also be u~ed. Radicals produced by photo reactions o~ the kind which occur on irradiation with W light or a~ and X rays with and without sensitizers, ir desired in the presence of peroxides, may al~o be employed. Suitable ;I water-soluble initiators include hydrogen peroxlde and the alkali metal and alkaline earth metal salts o~ per acids and peroxo acids. Ammonium and potas8ium peroxydisulphate are pre~erred.
Polymerisation may, o~ course, be started with the aid o~ redox 8ystem8. In this caæe, combinations of ~¦ hydrogen peroxide with reducing agents such as ascorbic acid and heavy metal salts such as iron or copper ~alts ~¦ 20 may be particularly recommended in addition to combinations -! such as potassium or ammonium peroxydisulphate and alkali ~ metal pyrosulphite at pH 4 to 6. The initiating system ¦ may be widely varied to produce special e~fects, see ~ouben-Weyl, Methoden der Oranischen Chemie, Volume XIV/2 t 25 in which initiators and redox systems are described. The concentration oi~ initiator is from 0.001 and to 10~ by ~! weight, based on the monomers~ preferably 0.05 to 0.4% by weight.
Polymerisation i8 carried out at a temperature between -40C and 250C depending on the selected initiator system :~ Le A 15 422 - 4-,'`
;

-iOS~994 and preferably in the range of 40C to 150C and at pressures which may be above 100 bar but are preferably between normal pressure and 25 bar.
The copolymers according to the invention may be 5 prepared by polymerisation in organic solution or suspensionr by emulsion or suspension polymerisation in an aqueous phase or by solvent-free polymerisation (for example in an extruder).
If the process according to the invention is carried 10 out in aqueous suspension it is necessary to use dispersing agents to obtain satisfactory bead polymers. The dispersing agents used may, for example, be polyvinyl alcohol, partly saponified polyvinyl acetates or cellulose or starch derivatives such as methylcellulose, ethylcellulose or 15 ethyl hydroxycellulose. The following are examples of ~ suitable synthetic dispersing agents (copo~yme~ of hydro-j philic and hydrophobic monomers): Styrene/acrylic acid;
~, styrene/maleic anhydride; ethylene/acrylic acid; ethylene/
maleic anhydride; acrylic acid ester/acrylic acid;
20 (meth)-acrylic acid derivatives/(meth)acrylic acid copolyme~s;
polyethylene oxides; ethylene/propylene oxide copolymers and polyesters with hydroxyl numbers between 10 and 250.
If mixtures of dispersing agents and emulsifiers are used, it is preferred to select emulsifiers which are biologically 25 degradable. Inorganic colloids or inorganic salts (for example phosphoric acid derivatives) may also be used.
Thio aqueous suspension polymerisation process may also be carried out as a reverse emulsion polymerisation or it may be started as a reverse emulsion polymerisation 30 and completed as a suspension polymerisation of styrene Le A 15 422 - 5 -lV56994 and acrylonitrile in water A solution of the monomers and a radical forming agent (organic phase) is produced by this process. Water 18 subsequently added to the organic phase and a water-in-oil emulsion is produced, preferably with the aid oi ; a water-in-oil emulsifier. The initiator or initiator m~ system may also be present in the water. In the system which i8 to be polymerised, therefore, the di~persed phase originally comprise~ water which may contain all or part oi the initiator or initiator system, portions Or the monomers and the water-in-oil emulsifier, while the ..
: remaining monomers or all the monomers constitute the I continuous phase. Copolymerisation may already set in

3 at the stage oi the preparation of the water-in-oil emulsion. Aiter iormation Or the water-in -oil emulsion . .
(iirst stage) an additional quantity oi water and, optionally, dispersing agents ior the water-in-oil `; ` emulsion are added with stirring (second stage), phase reversal gradually taking place at this stage. An i 20 oil-in-water dispersion is formed in which the water substantially forms the continuous phase and oil the dlspersed phase. At the end o$ polymerisatlon, the oll droplets dlspersed in water have completely solidified to porous beads which contain water.
. 25 The water-in-oil emulsifiers, which are preferably used . in quantities of 0.05 to 10 % by weight, more preferab ly 0O5 to

4% by weight, based on the monomers, may, ior example, ~` be graft products of styrene or other vinyl monomers on - polyethers or ethlene oxide or styrene copolymers with ~ ~-unsaturated carboxylic a~lds or a 1:1 copolymer of Le A 15 422 - 6 -11)56994 methacrylic acid and methyl methacrylate. Other water-in-oil emulsifiers are also suitable, for example those described in British Patent Specification No. 928,621 publi~hed June 12, 1963;
962,699 published July 1, 1964; 959,131 published May 27, 1964;
964,195 published July 15, 1964 and 1,076,319; German Patent Specification No. 1,300,286 published July 31, 1969 and 1,211,655 published March 3, 1966 or in Belgian Patent Specification No.
785,091 published December 19, 1972, all in the name of Farben-fabriken Bayer AG.
The proportion by weight of aqueous phase to organic phase should preferably be between 0.2:1 and 1:1 at the stage of preparation of the water-in-oil emulsion (first stage). These l;nnts may be exceeded in either direction so long as a water-in-- oil emulsion can be formed but the ratio of aqueous phase to organic phase should not be higher than 3:1. For preparing the water-in-oil emulsion it is always advisable to add the aqueous phase to the organic phase.
The aliphatic noolefins may be added with the solu- ~
tion of monomers or at a later stage but at the latest before phase -reversal takes place.
The polymerisation temperatures in the first stage are ` preferably 30 to 120C, more preferably 60 to 85C. Polymerisation is preferably continued to a conversion of 10 to 60%.
In the second stage, the proportion by weight of aqueous phase to oil phase is preferably between 1:1 and 3:1 and should not be higher than 10:1. Preparation of the water-in-oil emulsion may be carried out at temperatures of 10C to 90C. Addition of water and dispersing agent, if any, in the second stage is carried out after formation of the water-in-oil emulsion and heating or cooling to the polymerisation temperature of the second stage of 40 to 180C, preferably 75 to 150C.

i _ 7 _ , ~" ' .'" ''' ' ,., -1~56994 Dispersing agents which have been found suitable are polyvinyl alcohol, partly saponified polyvinyl acetate, alkyl celluloses such as methyl cellulose, alkyl sulphonateæ or alkyl sulphates . They are preferably used in quantities of 0.01 to 3 %
~i 5 by weight, more preferably 0.5 to 2 % by weight, based on the 7 quantity of monomers used.
~ A particular advantage of this process lies in the ; ease with which the porous bead polymer obtained can be processed and dried.
When the polymer is treated by thermoplastic processes the shaped products obtained have an exceptionally attractive surface gloss and are highly transparent with very little self coloration.
If the process according to the invention is carried ~} 15 out in one of the usual organic solvents, polymerisation .~ is stated in a homogeneous phase consisting of the monomers,the selected initiator system, the solvent and the aliphatic monoolefin. If the solvent is one which does not dissolve the polymer formed, polymerisation is completed as a precipitation or suspension polymerisation.
Suitable organic solvents include saturated aliphatic or aromatic hydrocarbons, substituted aromatic compounds such as toluene or chlorobenzene, halogenated aliphatic hydrocarbons such as methylene chloride, carbon tetra-chloride, trichloroethylene, tetrachloroethylene or trichlorofluoromethane or other frigens, low boiling alcohols such as methanol, ethanol, propanol, isopropanol and the isomeric butanols, preferably tert.-butanol, as well as dimethylformamide and dimethylacetamide.
If the process according to the invention is carried .~ .

Le A ~5 422 - 8 -: .
.... . . .

11~565~94 .
out as an emulsion polymerisation, it i9 distinguished not only by the fact that the monomers and initiator solution containing emulsifier may be added simultaneously 90 that exceptionally high output rates can be achieved at the preferred temperature region of about 80C and chemically very uniform products can be obtained, but also by an unexpected improvement in the molecular homegeneity which could nOt be achieved by an exact supply of the monomer alone.
According to a preferred embodiment of the invention, polymerisation is carried out at 75 to 85C. As already mentioned in United States Patent Specification No. 2,559,155 issued July 3, 1951 to Monsanto Chemical Campany, polymerisation at 80C under reflux conditions can very easily be controlled at a constant temperature.
The emulsifiers used may be alkali metal salts of modi-fied resinic acids, for example Dresinate ~ 731, but alkyl sulphates and sulphonates containing 12 to 24 carbon atoms in the alkyl group may also be used. Biologically degradable em7ulsifiers are preferred The emulsifiers are preferably used at a concentration of 0.5 to 20% by weight, more preferably 0.5 to 3% by weight, based on the aqueous phase. These emulsifiers may, of course, be combined with the above mentioned dispersing agents as desired.
The polymer may be isolated if desired by precipitation from the emulsion by known methods or, for example, by spray dry-ing.
The process according to the invention may be carried out continuously or discontinuously. Copolymerisation may be carried out with or without solvents in polymerisation apparatus such as extruder screw~, kneaders or special stirrer assemblies.
Evaporation of the solvents from the _ g _ , .
:
.
. ~ . . :. , - , polymerisation mixtures is carried out in evaporator screw~, thin layer evaporators or spray driers. The polymerisation reaction mixtures l.iay contain the usual auxiliary agents such as chain transferring agents for telomerisation reactions, molecular weight regulators if any are desired in addition to the aliphatic monoolefins, stabilizers, lubricants, antistatic agents and antioxidants.
-j Owing to their exceptionally uniform chemical structure and the fact that they have only a slight self coloration, the thermoplasts produced according to the invention can be dyed to exceptionally brilliant tones with the known dyes or pigments. The products according to the invention , are generally obtained as powders or beads, depending on the method by which they have been produced. They are used for the production of shaped products of all kinds and are exceptionally suitable for the production of articles which will come into contact with boiling water. They are also excep-tionally resistant to petroleum hydrocarbons and oil. Copolymers ~i may also be used for the production of films, fibres or coatings.
me products of the invention may be combined in various ways with fillers such as sawdust, chaIk, powdered glass or glass , fibres, for the production of novel high-quality materials.Their solutions or emulsions may, of course, also be used as coatings. The products of the invention can also be used as thermoplastic adhesives.
In the following examples, % means percent by weight an~i parts ~eHns parts by weight.

Le A 15 422 - 10 -.

ioS~994 E-Yample 1 111 g of styrene, 45 g of acrylonitrile, 2400 ml of water~ 63 g of Dresinate ~ 731 and 0.44 g of potassium peroxydisulphate are heated to 80C and stirred in a 6 litre vessel while isobutylene is introduced, and stirring is continued rOr 30 minutes at 80C. 10 ml of solution 1 and 80 ml of solution 2 are then added at intervals o~ 5 minutes.
Solution 1: 12 g of Dresinate ~ 731 and 3.86 g of potassium peroxydisulphate made up to 200 ml with water Solution 2: 999 g of styrene and 385 g of acrylonitrile.
Stirring is continued for 1 hour at 80C after all the reactants have been added. A total of 50 g of iso-butylene is passed through the reaction vessel. The latex has a solids content Or 39%. The reaction mixture iB precipitated and the polymer iB isolated and dried.
1443 g Or styrene/acrylonitrile copolymer are obtained.
According to the nitrogen content of N = 7.0% found by analysis, the acrylonitrile content is calculated to be 26.5%. The intrinsic viscosity determined in dimethyl formamide at 25C is (~) = 1.06, the K value according to Fikentscher is 69 and the dimensional stability under heat according to Vicat is 117C (according to DIN 53460 ; 25 at 5 kp loading).
Example 2 111 g of styrene, 90 g of acrylonitrile, 2400 ml of water~ 32 g of Dresinate(R)731, 32 g of sodium alkylsulphonate containing 12 to 14 carbon atoms in the alkyl group and 0.88 g of potassium peroxydisulphate are heated to 80C and Le A 1,5 422 iO56994 stirred while isobutylene is passed through. Stirring is then continued for 30 minutes at 80C and 10 ml of solution 1 and 80 ml of solution 2 are added to the reaction mixture at intervals of 5 minutes.
Solution 1: 12 g of Dresinate ~ 731 and 4.2 g of potassium peroxydisulphate made up to 200 ml with water Solution 2: 999 g of styrene and 340 g of acrylonitrile.
Stirring is continued for one hour at 80C after all the reactants have been added. A total of 50 g of isobutylene is passed through the reaction mixture. The latex has a solids content of 37.3%. After isolation and tr,?atment 1534 g of styrene/acrylonitrile copolymer are ; obtained. According to the nitrogen content of N = 7.55%found by nitrogen analysis, the acrylonitrile content is calculated to be 29.0%. The intrinsic viscosity determined in dimethylformamdie at 25C is (~) = 1.37, the K-value according to Fikentscher 81 and the dimensional stability under heat according to Vicat 114C.
ExamPle 3 1554 g of styrene, 511 g o~ acrylonitrile, 16,800 ml of water, 196 g of sodium alkylsulphonate containing 12 to 14 carbon atoms in the alkyl group, 0.7 Or ~l iron-II-ammonium sulphate, 1.9 ml of normal sulphuric ;~ 25 acid, 0.35 g of sodium pyrosulphite and 1.2 g of ammonium peroxide sulphate are introduced into a 40 1 stirrer ,t autoclave. The autoclave is evacuated and flushed with nitrogen. 600 g o~ propylene are then forced in. The reaction mixture is heated to 600C and stirred for 20 minutes at 60C. Three solutions are then added in ~:, Le A 15 422 . -12-., .

lOS~;994 a (ontinuous flow Solution 1: 42 g of sodium alkylsulphonate and 2.8 g oi ; sodium pyrosulphite made up to 1015 ml with water Solution 2: 16. 8 g of ammonium peroxydisulphate made up to 980 ml with water.
Solution 3: 6216 g of styrene and 2058 g of acrylonitrile.
Length of time during which the solutions are pumped in:
Solution 1: 180 minutes Solution 2: 165 minutes 1 Solution 3: 150 minutes.
;1l Stirring is ~ontinued for one hour at 60~C after the 3 addition of solution 1 has been completed. 6320 g of ~- styrene/acrylonitrile copolymer are obtained when the reaction product is processed. According to the nitrogen content of N = 5.95 determined by analysis, the acrylonitrile ~ content is calculated to be 22.6%. The intrinsic viscosity t oi the polymer in dimethylformamide at 25C is (~)= 1.72, the K-value according to Fikentscher 89 and the dimensional i 20 stability under heat according to Vicat is 110C.
' ExamPle 4 j 6720 g of styrene, 2226 g of acrylonitrile, 24 g oii tert.butylperpivalate, 850 ml Or an 8~ solution of dispersing agent (1:1 copolymer of methacrylic acid/methyl methacrylate in aqueous solution adjusted to p~ 6), 8500 ~ ml Or water and 2.8 g of sodium pyrosulphite are introduced ? into a 40 1 stirr0r autoclave. The autoclave is evacuated and flushed with nitrogen. 400 g of propylene are then ~ introduced. The reaction mixture is heated to 80C and 3 30 a solution of 6.3 g of a sodium alkylsulphonate containing Le A 1~ 422 -13-..

- 105~994 1) to 14 carbon atoms in the alkyl group in 10,500 ml oi water are then continuously pumped in ior 4 hours at 80C. The reaction mixture is then stirred ~or a iurther 2 hours ~t 80C. Unreacted monomers remaining behind and volatile constituents are removed with steam. The bead polymer is washed and dried. 7710 g oi a copolymer with an acrylonitrile content of 23.5%, a styrene content oi about 76% and a propylene content below 0.5% are obtained.
The intrinsic viscosity (~) determined in dimethylformamide at 25C i9 1 . 4 and the dimensional stability under heat according to Vicat is 111 to 112C.
I Example 5 } 650 g of styrene, 170 g Or acrylonitrile, 40 ml oi a 10% solution oi dispersing agent (1:1 copolymer of methacrylic acid and methylmethacrylate adjusted to pH 7), 1000 ml oi water and 0.4 g oi sodium pyro~ulphite are heated to 80C in a 6 1 stirrer vessel and stirred while iso-butylene is passed through. Stirring is continued ior a iurther 15 minutes at 80C and 2.2 g oi a 75% tert.-butyl perpivalate solution in dibutylphalate diluted with 15 ml oi cleaning petrol are then added. At the same time, .1 addition oi the iollowing solution, which takes 100 minutes is begun: 60 ml oi a 3% solution oi polyvinyl alcohol with I a molecular weight oi 30,000 and 6 g oi sodium dihydrogen 3 phosphate made up to 1000 ml with water.
::
. The reaction mixture is then stirred for a iurther 2 hours at 80C. 100 g oi isobutylene are passed through the reaction mixture during this time. Unreacted monomers i remaining in the reaction mixture and volatile constituents are removed by stripping with steam. The bead polymer is .` -Le A 15 422 -14-_, , .. .

l(~St;994 - isolate(l, washed and dried. 770 g of a styrene acrylo-nitrile copolymer with an acrylonitrile content Or "0.2% (5.4% N), a styrene content of 79.7~ and an iso-butylenc contcnt of about 0.1% are obtained. The dimensional stability under heat determined according to Vicat is 107 to 10~C. The copolymer was dissolved in acctone/dimethylformamide and precipitated portionwise with petroleum ether. The intrinsic viscositieg of the resulting five fractions in dimethylformamide at 25C
and their nitrogen contents were determined. The following results were obtained:
Fraction No. % by weight Acrylonitrile ~ by weight ~ ' 1 15.6 3.12 20.4 2 22.63 1.80 20.4 3 18.03 1.14 20.1 4 15.05 0.82 19.8 4.36 0.42 24.6 In spite of the quantities oi styrene or acrylonitrile put into the process over and above the azeotropic proportions oi styrene and acrylonitrile (see ~ouben-Weyl, Methoden der Organischen Chemie, Georg Thieme-Verlag, Stuttgart., 1961, Vol.XIV/2, page 841), a chemically extremely uniiorm copolymer is obtained whereas a suspension polymer prepared under the same conditions without using -oleiines as regulator was chemically much less uniform.
` Example 6 1998 g of styrene, 630 g of acrylonitrile, 120 ml oi a 10% solution of a dispersing agent (see Example 2) ~` .
Le A 15 422 -15-. . ,~ , :
: . . . . .

105~;994 150 ml of a 5% solution of polyvinyl alcohol (Molecular Weight 30,000), 4.97 g of benzoyl peroxide, 5000 ml of water, 1.2 g of sodium pyrosulphite and 18 g of sodium dihydrogen phosphate were introduced into a 12 1 stirrer autoclave. The autoclave was evacuated and ~lushed with nitrogen. 2000 g of propylene were then forced in.
The reaction mixture was heated to 85C and stirred for 6 hours at 85C. Processing of the reaction product yields 2240 g of a copolymer with an acrylonitrile content o~ 23%, a styrene content of 76.9~ and a propylene content of 0.1%. The intrinsic viscosity of the copolymer determined in dimethylformamide at 25C is ~ = 1.38.
The dimensional stability of the copolymer under heat according to Vicat (DIN 53 460) is 109-110C.
-I 15 ExamPle 7 '~ Comparison test A) 740 g of styrene, 300 g o~ acrylonitrile, 12000 ml o~ water, 315 g o~ Dresinate(R)731 and 2.9 g of potassium peroxidisulphate are introdoced into a 40 1 stirrer autoclave under nitrogen. The autoclave is evacuated and ~lushed with nitrogen. The reaction mixture is heated to 80C and stirred for 30 minutes . .
at 80C. Two solutions are then pumped in simul-taneously over a period of 3 hours.
Solution 1: 80 g of Dresinate(R)731 and 25.7 g o~
potassium peroxydisulphate made up to 1500 ml with water Solution 2: 6660 g of styrene and 2567 g Or acrylonitrile.
The reaction mixture was then stirred ~or one hour at 80C and coagulated with salt solution. 8500 g of a copolymer with an acrylonitrile content of 23~ and an Le A 15 422 - 16 -intrinsic viscosity of 2.22 in dimethyliormamide at ~;l 25C are obtained. The soitening temperature according I ' to Vicat is 104C and the melt index determined at " ` 240C under a load oi 10 kp is 12 [g/10 min].
These products are diiricult to process thermo-plastically because oi their poor flow characteristics.
B) Comparison test ~i ! A SAN copolymer prepared under similar conditions in the presence Or 0.4% oi dodecylmercaptan as regulator contains 26~ oi acrylonitrile and has an intrinsic ' viscosity of 0.89 in dimethyliormamide at 25C and a !,~ melt index at 240C/10 kp load oi 172 (g/10 min).
r . ~
'; The Vicat sortening temperature is 104C.
C) A copolymer prepared under similar conditions in the presence oi 1.9~ oi isobutylene contains 26~ oi acrylonitrile and has an intrinsic viscosity in di-methyliormamide at 25C oi [~ - 1.08. The melt index at 240C under a 10 kp load i8 162 [g/10 min], and the Vicat soitening temperature is 116C.
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Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Process for the production of styrene (meth)acrylonitrile copoly-mers with improved dimensional stability under heat in a homogeneous or heterogeneous phase, wherein a mixture of (meth)acrylonitrile and styrene containing a radical forming agent is polymerised in the presence of at least one aliphatic monoolefin with 2 - 18 carbon atoms, the amount of aliphatic monoolefin present being such that in the styrene (meth)acryloni-trile copolymer obtained the aliphatic monoolefin content is from 0.1 to 1.9% by weight, based upon the weight of styrene (meth)acrylonitrile and aliphatic monoolefin.

2. A process as claimed in claim 1, wherein the aliphatic monoolefin contains from 2 to 4 carbon atoms.

3. A process as claimed in claim 1, wherein the aliphatic monoolefin is ethylene, propylene, butene-1, butene-2, isobutylene, a straight or branched chain pentene, a hexene, an octene.

4. A process as claimed in claim 1, wherein radical forming agent is a per compound or an azo compound.

5. A process as claimed in claim 4, wherein the radical forming agent is an aliphatic azo dicarboxylic acid derivative, an azodicarbonamide, an azodicarboxylic acid ester, a peroxide, a ketone peroxide, an alkyl ester of a per acid, a dialkyl peroxide, a hydroperoxide or a per acid.

6. A process as claimed in claim 1, wherein the polymerisation is carried out at a temperature of from -40 to 250°C.

7. A process as claimed in claim 6, in which the polymerisation is carried out at a temperature of from 40 to 150°C.

8. A process as claimed in claim 1, wherein the polymerisation is carried out at a pressure of between normal pressure and 25 bar.

9. A process as claimed in claim 1, wherein the polymerisation is carried out in organic solution or suspension, by emulsion or suspension polymerisation in aqueous phase or by solvent-free polymerisation.

10. A copolymer containing a) 5 to 85 % by weight of acrylonitrile or methacrylonitrile, b) 14.99 to 93.1 % by weight of styrene and c) 0.01 to 1.9 % by weight of an aliphatic monoolefin, whereby the sume of the components a), b) and c) is 100-

11. A copolymer as claimed in claim 10, which contains from 10 to 40 % by weight of (meth)acrylonitrile and from 89.99 to 58.1 % by weight of styrene.