CA1131839A

CA1131839A - Mixtures of rubber with graft copolymers

Info

Publication number: CA1131839A
Application number: CA303,339A
Authority: CA
Inventors: Eberhard Muller; Karl-Heinz Ott; Wilhelm Gobel; Gottfried Pampus
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1977-05-17
Filing date: 1978-05-15
Publication date: 1982-09-14
Also published as: FR2391242B1; JPS53141352A; ES469932A1; DE2722403C2; BE867092A; IT1103146B; DE2722403A1; NL184689B; NL184689C; FR2391242A1; NL7805263A; JPS6118578B2; IT7849346A0; GB1600676A

Abstract

Abstract of the Disclosure Rubber mixture are disclosed wherein a graft copolymer (B) is mixed with a rubber (A) in an amount from 1 to 80% by weight, and wherein the graft monomers of (B) are identical of compatible with the monomers of the rubber (A) used for mixing.

Description

33~3 The present invention rel~te6 to rubber mixtures ~nd more particularly relates to rubber mixt.ures wh~rein a gra~t polymer ~B) is added to a ~Ibber (A) :in qu~ntities of from 1 to 80~ by weight, the monomers Or (B) which ~re used ~or grafting being identical or comp~tible with the ~ono~ers of the rubber (A) used for mixing.
~ ixtures of rubber ~ith other rubbers vr the~mopl~sts are known in many conceivable v~ri~-tions ~nd are described in the relevant literature. See ~or ex~ple Rubber Chem.
Techn. 47 ~3) 481-50, 1974 and Rubber Chem. Techn, 49 (1), 93-104 (1976).
Such mixtures ~re gener~lly used to achie~e a balanced r~tio between proc~ssing prop~rties, service properties and costs. As far as the service propertie~ are concerned, this means ior ex~mple that, in ~any cases, a specifio t~pe of rubber is regarded as unsuitable for a cert~in ~pplioation, whereas another property of the s~e ~Ibber is highly desirable.
Thus 9 cert~in rubbers are blended with one ~nother in order to additionally obt~in desirable properties ~nd to reduee undesir~ble properties.
Because of the well known serious incompAtibility o~
polymers wîth one ~nother, there are numerous limitations in the production o~ polymer mixtures, see ~or ex~mple,.
Kolloid-Zeitschrift u. Zeitschrift ~. Polymere, VQ1~ 213, 1966, Lothar Bohn and J~ MQcro;nol. Sci.-Rev~. Macromol. Che~. 9 C7 (2), ~51-~14 ~1972).
As a result o~ incompatibilities, deteriorations gener~lly occur in the technologic~l properties o~ rubber-ru~ber mi~tures Le A 18 040 - 2 3''.~

(~or ex~mple reduct10n o~ the tensile ~trength of mixtures of polybut~diene with polych10roprene or nitrile rubber) or rubber-thermopl~st mi~ture~ ~for ex~DIple reduction in the elong~tion at break o~ mixtures of polyethylene and n~tur~l rubber or polystyrene ~nd polybut~diene). Considerable reduction~ in tensi1e stren~th and te~r propagatlon resist~nce are also observed ~or example in~t~ ease of mixtures of thermopl~stic styrene~butadiene three~block po1ymers with po1ybut~diene or polyethylene.
Gener~lly, it ~ay be s~id th~t, in the case of co~p~tîble polymers~ the properties o~ the ~ixtures v~ry substanti~lly line~rly with their composition. Th1s ~pplies only, howeYer, to compatible mixtures~ Incomp~tible poIy~ers c~n on1y be mixea ~ith one another when important properties o~ the polymer to be mofli~ied ~re not too seriously a~ectea.
It has now been found that rubber ~A~; prefer~bly ~ diens or olefin rubber or their copolymers, can be mixed with oth0r polymers when certain gr~t polymers (B) are used ~or mixi~g in qu~ntities of from 1 to 80~ by weight, $he base of the graft polymer (B) being grafte~ with monomers which ~re identical or compatible with the ~ono~er~ of the rubber (A) and ~hich conveniently ~y be crosslinked together with th~
rubber (A) in the ~ixture. It is also possible to use di~ferent mo~omers for gra~ting. In t~is way, ther~ is obt~ined a new type o~ ~Ibber in which a regular~ locally fixed distribution o~ graft po:ly~er particles i5 present.
~lc~ ed ~bber ~ Aceordingly, the present invention pro~i~es a~ ixture : of rubbers (A3 and gra~t polymers (B) in quantities of ~rom Le A 18 040 - 3 ~
'~ ' ~`

~9 to 20 parts by weight (A) and :I to 80 parts by welght {B), said grat copolymer (~) having a parti.cle s:ize o:E from 0.1 to 2 ~m and having been p:roduced by polymeri~atioll of grafting base and grafting monomer in the presence of a radical ;.nit:i.ator; sai.d rubber (A) being selected from natural rubber, polybutadi.ene, polyisoprene, polychloroprene, butadiene-styrene copolymer, isoprene-styrene copolymer, butadiene-acrylonitrile copolymer, butadiene-isobutylene copolymer, isoprene-isobutylene copolymer, ethylene-propylene copolymer, polyisobutylene, ethylene-vinylacetate copolymer and acrylate rubbers; the graft base of said graft copolymer (B) being at least one member selected from polybutadiene, polyisoprene, polychloroprene, natural rubber, styrene-butadiene copolymer, acrylonitri.le-butadiene copolymer, styrene-isoprene copolymer, polystyrene, s~yrene-acrylonitrile copolymer, ethylene-propylene copolymer, ethylene-propylene di.ene terpolymer, polyiso-butylene, isobutylene-isoprene copolymer, polymethylacrylate, polyethylacrylate polypropylacrylate, polybutylacrylate, polymethyl methacrylate, ethylene-vinyl-acetate copolymer, polycarbonate, polyethylene, polypropylene, polyvinyl-chloride and cellulose esters; and the grafting monomer of the graft copolymer ~B) being identical to or compatible with the monomer of rubber (A) and being at least one monomer selected from butadiene, isoprene, chloroprene, isobutyl-ene, butadiene/styrene, butadiene/acrylonitrile, isoprene/styrene, isoprene/isobutylene, methylacrylate, ethylacrylate, propylacrylate, butylacrylate, isoprene/butadiene~ chloroprene/isoprene and isoprene/acrylonitrile. The i.nvention also provides a process for producing said mixture.
In contrast to all hitherto known rubber mixtures, it is possible with a rubber mixture of the present invention to establish a morphology of a multiphase rubber system which is largely independent of the mixing conditions ~mixing rolls~ internal mixer, solution).
Preferred rubbers (A) are selected from polybutadienes, polyisoprenes, butadi.ene-styrene copolymers butadiene-acrylonitrile copolymers, isoprene-isobutylene copolymers, ethylene-propylene copolymers and polychloroprenes.

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~I;xtures of the above graEt polymers ~B) may also be used as the gra:Et base.
lhree or more of the ~raEt mollomers :Eor producing the graft copolymer (B) may be grafted into the mixture to obtain better compatibility.
For the purposes of illustration, the following mixtures are mentioned by way of e~ample:
For mi.xing with polychloroprene as rwbber ~A), the following polymers may be gra~ted with chloroprene: po~ychloroprene, polybutadiene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, styrene-i.soprene .
copolymers, polystyrene, styrene-acrylonitrile copolymers, and ethylene~
propylene copolymers; the following polymers are preferably grafted with butadi.ene and/or isoprene for mixing with polybutadiene, as rubber (A):
polystyrene, acrylonitrilebutadiene copolymers, polychloroprene, styrene-acrylonitrile copolymers, and ethylene-propylene copolymers; the following polymers are preferably grafted with isoprene or butadiene and acrylonitrile for mixing with butadiene-acrylonitrile copolymers as rubber ~A): polybutadiene, polyisoprene or polystyrene or their ' ~.

~l~3~3~3 copolymeTs, ~nd ethylene-propylene copolymers; -the following polymers ~re preferably grafted with isobu-tylene ~or mixing with polyisobutylene as rubber (A)~ pQlysl;yrene9 styrene-~crylonitrile copolymers, and polychloroprene. the following poly~ers are preferably grafted with isoprene and/or butadiene and/or lsobutylene or chloroprene with i~oprene ~nd/or butadiene and/or butadiene and/or isobutylene for mixing with ethylene-propylene copolymers as rubber (A)-polystyrene,~polybutadiene, polyethylene, polycarbo~ate ~nd butadiene-~crylonitrile copolymers, and also styrene-acrylonitrile copolymers~
Different rubbers (A) may also be made miscible with one another by ~ixing in one or more graft copolymers.
Naturally the~examples given above only show some o~ the nu'merous possibilities of producing co~patible ~ixtures.
The graft copolymers ~) which may consist of one or ~ore di~ferent graft copolymers ~re added to the rubber (A) in quantities of from 1 to 80~ by weigh-t and pPe~erably in quantities of ~ro~ ~ to 30% by weight. The graft monomer of the gra~t polymer (B~ may be used i~ a quantity o~ ~rom 10 to 80~ by weight, preferably in a quantity o~ from 30 to 60~ by weight, based on the graft base.
The molecular weight of the chain o~ the graft br~ches may be o~ the order o~ ~rom 5000 to 1,000,000 and preferably -from 20,000 to 150,000 (~s measured by the light scattering method).
~he graft monomer may be crosslinked, but a low degree of crosslinki~g is preferred. The graft base may be crosslinked ke A 18 040 ~ 6 ~

33~3 or uncrossL:inked, althou~ll i-t is pre.eerably crosslink~d.
The graI't polymer (B~ has a pArtic:l~ size of Irom 0.1 to 2~m, preferably ~rom Ool -to 0.8 ~m.
The gra~t po.lymcrs (B) may be prc,duced by radical solut~on, or by bulk, suspension or emulsion polymerisation5 irrespectiv~ of the~ tor used~ at t,empe~a-tures of from ~2VC to 120C. It is preferred to adopt a process in which .
the graft polymer is obtalne~ in a form in which it can be favourably mixed with the r~bber (A). For e:~ample, in cases where a rubb~r (A) produced by solution polymerisation, such as for c~alDple cis-194~olybutadiene or an ethylene-propylene copolymer, is, to be mixed with a graft polymer (B), the graft polymer (B) used will be a graft polymer which has been produced in ~1 solution which is identical or miscible with the solvent used in the production o~ the rubber (A)~
If for example a rub~er ~A) produced by emulsion polymerisation, such as an emulsion st~rene butadiene copolymer or polychloroprene or a butadiene acrylonitrile copolymer, is to be mixed with a graft polymer (B) 9 it is preferable to use an emulsion process ~or producing the graft polymer (B)~
Bases having an aver~ge particle size of from 0.05 to 1 ~, pre~erably from 0.1 to 0.4 ~, ~re used for the production of graft latices.
If it is desired to produce gra~t polymers ~) haYing ~ base which normally contains no doublc bonds, hydrogen atoms or heterogenous groups which are suitable ~or gra~ting, bases are synthesised by copolymerisation with certain Le A 1~ 0ll0 - 7 eomc)rlomcl~ sllitR`ble for gl~nIt polymerisation (for exarnplo styl~ene is copolymeri~c(l ~ith isoprene or butadiene in quantities O:e from 5 to 2~
A number o-L` desir~ble technological ~roperties can be o`btainecl by suitable mixtures of rubber (A) and gr~Et polymer (B). For example, the strength9 moduli and processi-bili~y of polychloroprene rubbers can be improved accordingly by ch~oroprene-gra~ted polystyrene or styrene/acrylonitrile copolymer. By mixing chloroprene-grafted polybutadiene with polychloropre~e, its low-temper~ture flexibility is increased.
By mixing chloropr~ne-gra~ted butadie~e/acrylonitrile copolymer with polychloroprene, its resistance to oil is ~lproved~
By mixing butadLene- or isoprene-grafted polys~yrene with polybutadiene or ethylene-propylene rubbers, their strength and processibility are improved. By mixing isoprene- or butadiene/acrylonitrile~grafted butadiene or i~oprene, the low-temperature flexibility o~ butadiene/acrylonitrile copolymers is increased. o These examples may be continued ad in~initun and the aboYe are by way o~ illustration only The important ~actor in every case is that~ by virtue of the grafting-induced compa~ibility of the graft copolymers with the rubbers, it ia possible to obtain a controlled modi~ication of certain technological properties without the characteristic properties ~5 of the base rubber (A) being undesirably in:Eluenced to any significant extent.
The rubber (A) may be mi~ed with the gra~t polymer (B) ~e ~ lB 040 - 8 -~3~

in diIferent ways:
For ex~mple, it is possible to mix the corresponding latices at room temper~tllre or at el~vated temperature ~nd then to congulate the resulti~g mixtures by adding salts~
acids or alcohols, or to precipita-te the rubber mi~ture by low-temperature coagulatio~. It i~ also possible to mix the dissol~ved pol~mers (A) and (B) ~nd to work up the solution by stripping, spray d~ying or precipitation~ for example with alcohol. For the sake of comp1eteness, re~e.rence is ~lso made to the possibility of mixing latex with solution.
Mixing may also be carried out mechanic~lly o~ mixing rolls, in internnl mixers or in screw extruders at temperatures in the range ~rom 20 to 120C.
Fillers, extenders and vulcanisation aids may also be incorporated duri~g the mixing oper~tio~s.
The mixtures of rubber ~A) and graft polymer (B) may be vulcanised ln the usual way in the presence of sulphur or peroxides.
The process accordlng to the invention is illustrated by the following Examples:
A~ Production o~ gra~t polymers B. Production o~ graft polrmer/rubber mixtures~
Ad A: The graft polymers used ~or ml~i~g with rubber are produced i~ emulsion, suspension or solution by means o-f radical initiators, EX~MPLE A 1 1600 g of polybutadi~ne latex ~solids content 540 4~, average particle size 0.4 ~) and 1640 ~1 o~ desalted water Le A 18 040 ~ 9 -are introduced in-to ~ (i litre fl.ask. The ~lask ls then purged with nitrogen an~ lts contents heated to 63-65C.
After heating, a solutlon o:f 4.5 g of potassium persulph~ke ln 200 ml of water ls added.
At 63 to 65C~ 540 g of chloroprene and a mixture of 375 g of water and 12 g of an emulsifier of the alkyl sulphonate type are separately and sl~ultaneously added dropwise over a period oI 4 hours, followed by stirring for 4 to 6 hours at 63-65C.
After degassing, the latex is filtered and directly u~ed for mixing test~ with rubber lat~ces or solutions, EX~PLE A 2 1600 g o butadiene-acrylonitrile copolymer latex ~ o~ acrylonitrîle, DeYo hardne~s 1000, solids co~centration 49 5~ particle size 0.2 ~) and 1640 ml of desalted water are introduced into a 6 litre flask.
The flask is then purged wi-th nitrogen and its contents heated to 63 - 65C. A~ter heati~g9 ~ solution o~ 4.5 g o~ !:
potassium persulphate in 200 ml of desalted water is added.
At 63 to 650~, 540 g of chloroprene and a ~ixture o~
375 g of water and 12 g of an emulsi~ier o~ the alkyl sulphonate type.are simultaneously and separately added dropwise over a period of 4 hours, followed by stirri~g for 4 to 6 hours at 63 to 65C. A~ter degas~ing, the ~atex is filtered.
EX~MPLE A 7 2260 g of polychloroprene latex (solids conc~n-tration 35.2 %, av~rage particle size 0~ /u) and 1000 ml of desalted water are introduced into a 6 litre flask, ~he fla.~k is t~en purged with nit~o~en and its con~ents heated to 63 - 65C. After heating7 a solution of 405 g o~
Le A 18 040 - 10 -__ .

~13~31~

potassium persulphate in 200 ml of water i~ added.
At 63 to 65C, 540 g of chloroprene and a mixture of 375 g of water and 12 g of an emulsifier of the alkyl sulphonate type are simultaneously and sep~rately added dropwise over a period of ~ hoursy ~ollowed b~ stirring for 4 to 6 hours, at 63 to 65C. After degas~ing, the latex i5 ~iltered.
EXAMPIIE A 1~
___ 1600 g of polybutadiene latex (solids content 54.4%, average particle size 0.4 ~) and 1640 ml of desalted w~ter are introduc~d into a 6 litre flask.
The flask is then purged with nitro~en and its contents heated to 63 - 650C. After hea-ti~g~ a solution of 4,5 g of potassium persulphate in 200 ml of water is added.
At 63 - 65C, a mixture of 378 g of isoprene and 162 g f acrylonitrile together with 375 ml of water and 12 g of an emulsifier of the alkyl sulphon~te type ~re simultaneously and separately added drop~ise over ~ period of 4 hours, fol'Lowed ~y stirring for 4 to 6 hours at 63 - 65C. After degassing, the latex is filtered.

1600 g of a butadiene-acrylonitrile copolymer latex (33% of acrylonitrile, Defo hardnese 1000, so:Lids concentration 49.3%, average partic:le size 0,19 ~) and 1640 ml of des~lted water are introduced into a 6 litre flask.
The flask is then purged with nitrogen and its contents heated to 63 ~ 65Co At 63- 65C, ~ mixture of 475 g of styrene and 65 g of acrylonitrile together with 375 ml of Le A 18 040 1'1 ~-.3~

wa-ter ~nd 12 g of an emulsi~ier of the alkyl sulphonats type nre simult~neously and separately added dropwise over a period of 4 hours, follQwed by stirring ~or 4 to 6 hours at 63 - 65C. After degassing~ the latex is filtere~
r EX~SPl.E A ~i ___ 1970 g o-f ~tyrene-~soprene copolymer latex (10~ o~
isoprene, solids content 40 8~, ~ver~ge particles size 0.15 and 1260 g of des~lted wa-ter are initially intru~ced into a 6 litre flas~.
The flask is then purged with ni~rogen and its contents heated to 63 - 65C. A-t 63 - 65C9 540 g o~ chloroprene ~nd a mixture of 375 g of water and 12 g o~ an emulsifier of the alkyl su:Lphonate type are simultaneously and separately added dropwise over ~ period o~ 4 hours) followed by s~irring for 4 to 6 hours at 63 - 65~o A~ter degassing, the latex is filtered.
' :
250 g o~ cis-1,4-polybutadiene ~ ~ 240 ml~g~ is added to 4 litres o~ toluene, followed by stirrlng until a solution is formed. 200 g of chlorophene, 200 g o~ isoprene and 12 g o~ benzoyl peroxide are then added, followed by stirrlng ~or 18 hours at 60C

5.2 litres o~ n-hexane and 320 g of ethylene-propylene :2S terpolymer (EN-type~ Mooney ML 4-100 90, 12 C=C-d~uble bonds per 1000 carbon atoms) are introduced into a 10 litre autocla~e, followed by stirring until the rubber has completely dissolved.

Le A 18 040 - 12 ~
__ ~L~3~L~33~

~l80 g o~ chloroprenc and a so`lution of 15.'~ g o~ dibenzoyl pero~ide in 100 ml o~ benzene are then added, followed b~r stirring for 18 hourc at 60C~
Ad B: The rubber ~nd gra~t polymer are mi~ed with each other in latex form, in solution or in solid form on mixing rolls or in all internal mixer. The latex mixtures ~nd the solutlon are worked up in kno~ manner ~y precipitation and stripping, respectively.
St~ndard c~rbon black mi~tures are initially produced -from the graft polymer mixtures in accordance with IS0 Speci~ic~tioll 2475-1975 ~E), ~ter which ~ouldings are produced ~rom the resulting mixtures and then pressvulcanised for 20, 40 and 60 minutes at a temperature of 150C. The necessary test specimens ~re cut ~rom the sheets obtained. Strength (F~l elong~tion (D) and strain values (S; at 100/300~ elongation) are tested on the Standard ~est Ring I according to DIN 53 504, whilst Shore hardness A ~H; a-t 20 and 70C~
is -tested in accordance with DIN 53~05 and resilience 2V (E) in accordance with DIN 53512. The compression set is measured in accordance with DIN 53517~ The crude graft polymer m-ixtures employed are used for measuring the polymer viscosity and the difference in viscosity between the one minute and the ~our minute value in a Mooney Tester at 100C (Ml-4) i~ accord~nce with DIN 53523 and De~o plasticity in accordance with former DIN 53514. The gel content is determined by centri~uging Le A 18 040 ~ 13 ~3~3~

a toluenc ~olutiorl, A selection of prepared and tested graft poly~er mixl;ures (I~.~X) is given and fully characterised in 'l'ables la ~nd lb. The test dat~ of the vulcanisates nre shown ln Table II.
F~MPLE B 1 (Table 1~) Polymer mixtures of 90 (I) and 80 (II) parts by weight o~ a chloroprene homopolymer with 10 and 20 parts by weight, respectiv~ly, of a chloroprene-grafted polystyrene have a distinctly higher gel content and viscos:ity trencl value, re~lected in better prccessing properties, in comparison with the pure chloroprene ho~opolymer (V).
The products also show high streng-th, strength and hardness ~alues in the vulc~nis~tes.
~ (Table la) Pol~mer mixtures of 90 (III) and 80 (IY) parts by weight of a chloroprene homopolymer with 10 and 20 parts by weight, respectively, of ~ chloroprene-grafted butadiene-~crylonitrile copolymer containing 38~ of acrylonitrile ~l~o show a higher gel content and viscosity trend value ~nd, hence, better processing properties ~y comp~rison with the pure chloroprene homopolymer (V). In the ext~usio~ of strln~sg output is higher axld the level o~ extrusion swelling lower.
A~ter agein~ in hot air (21 days/100C)~ the i~crease in the hardness and strain values ~ the vulcanisates containing the polymers according to the inve~tion is lower, i.e. they are more resistant to ageing. In addition, the ~ulcaxlisates ~e A 18 040 - 14 -~3~33~

cont~ining the polymers accordlng to the l~vention ars muoh more resistant -to ASTM oils~ ~s shown by storage test~ at 1.00C.
EXAMPLE ~ 3 (Tnble la) Pol~r mixtures of 85 (~ nd 70 (VII) pnrts by weight o~ a chloroprene homopolymer wi th 15 arld 30 parts by we:ight respectively~ of a chloroprene-grafted polybutadiene also show a much higher gel content and viscosity trend value and, hence, extre~ely good processing properties in comparison with the pure ho~opolymer (V)~
The vulc~nisates of the polymer mi~tures show hlgher hardness, strain and elastic~-ty values in compariso~ with the re-ference material.

EXAMPLE B ~ (Table la) . Polymer mixtures of 90 (VII13 and 80 (IX) parts by weight of a chloroprene homopoly~er with lO and 20 parts by weight, respectively, o~ ~ ehloroprene-gr~ed styrene~isoprene copolymer show higher gel contents and viscosi*y trend values and, hence, better processing properties in co~parison wit~

the pure chloroprene homopolymer (Y).
EXAMPLE B 5 (Table la) In comparlson with the ungrafted re~erence material (V)g a polymer ~ixture o~ 80 parts by weight of a chloroprene homopolymer with 20 parts by weight o~ a chloropre~e-gra~ted polychloroprene (X) also 3hQws higher gel contents and viscosity trend values ~nd9 hence9 better proce3sing properties. Higher strain, hardnes~ ~nd elasticity v~Lues are ob-tained in the Le A 18 040 lc~ _ ~ L3 vulc~ni sate .
EXAMPLE ~ 6 ~Table la) In compArison with the ungrafted re~erence material (XIII), polymer mixtures of 90 (XI) and 80 (XII) parts by weight of a sulphur-modified polychloroprene with l0 and 20 parts by weight, respectively, of ~ chloroprene-grafte~ polybutadiene si~ilarly to the product6 of the preceding Examples - show higher gel contents and ~iscosity trend values which enable rolled sheets to be rapidly ~ormed. In the carbon bl~ck mixtures, the products are less lnclined to become tacky on the rolls and pro~ote more rapid vulcanisation which leads to a higher crosslinking density with higher strain, hardness, el~sticity and compression set values.
~ tTable la) The polymer mixture of 80 parts by weight of a chl~ropr~ne homopolymer with 20 parts by weight of a chloroprene-grafted butadiene-acrylonitrile copolymer containing 38~ of acrylonitrile (IV b) shows ~ Mooney vi8c06ity ML-4~100C o~ 58 ME and a gel content of 16%.
In this respect, it is comparable with a so-called pre-crosslinked polychloroprene (IV a) which is obtained by mixing benzene-soluble homopolymers or copolymers of chloroprene with ben~ene-insoluble copolymers of chloroprene generally produced by known methods, e.g. British Patent No. 1,158,970, using diesterst and which is used in particular for applications requiring good processing properties. Howe~er, ~or e~uivalent processing properties of IV b and IV a, the polymer mixture according to the invention produces higher strength valuesf Le A 18 040 - 16 ___ 33~

better co~pression set and be-tter agei~g b0haviour.
EXAMPLE L 8 lTable lb) A pol~er mixtllre o~ 90 (XI~) and 80 (XV) parts by welght of a ch].oroprene homopolymer with 10 an~ 20 parts by weight, respectively, of a ehloroprene-grn~ed cis-1,4-poly~
butadiene has Mooney viscosities ML-4/100C ol 58 ~nd 68, and gel contents of 8 and 20% respoctively.
In the vulcanisa-tes9 the mixture ~hows excellent strengths ~nd elongations, good low-temperature flexibility and a low compression se~c EXAMP~E B 9 ~Table lb) In comparison with the pure homopolymer (V), a poly~er mixt~re of 80 parts by weight of a chloroprene homopolymer with 20 parts by weigh-t of a chloroprene-grafted ethylene-propylene terpolymer (XVI) shows a higher gel content and viscos.ity trend ~alue and, hence9 extremely good processing properties, An increased resistance to ageing is obtained in the vulcanisates.
EXAMPLE ~ 10 (Table lb) A polymer mixture of 85 (XVII) and 70 (XVIII) parts by weight of ~ nitrile rubber with 15 and 30 parts by weight, re:spectively, of an isoprene/acrylonitrile-gr~tea polybutadiene shows good strength and elongation values, incre~sed low-temperature flexibility and r~duced co~pression set.
EXAMPLE B 11 (Table lb) ____.
A polymer mixture of 90 (XIX~ and 80 (XX) parts by weight of a lithium polybutadiene with 10 and 20 parts by weight, respeetively, of an isoprene~grafted polystyrene shows good Le A 1~ 040 - 17 -3~3 ~tren~th An~l elo;l~ation vnlues and n very considerable improvement :in proces~:Lbllity over lt,he pure polybut~diene.

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Claims

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

1. A vulcanized rubber mixture comprising a rubber (A) in an amount of from 99 to 20% by weight and a graft copolymer (B) in an amount of from 1 to 80% by weight, said graft copolymer (B) having a particle size of from 0.1 to 2 µm and having been produced by polymerization of grafting base and grafting monomer in the presence of a radical initiator; said rubber (A) being selected from natural rubber, polybutadiene, polyisoprene, polychloroprene, butadiene-styrene copolymer, isoprene-styrene copolymer, butadiene-acryloni-trile copolymer, butadiene-isobutylene copolymer, isoprene-isobutylene copolymer, ethylene-propylene copolymer, polyisobutylene, ethylene-vinyl-acetate copolymer and acrylate rubbers; the graft base of said graft copolymer (B) being at least one member selected from polybutadiene, polyisoprene, polychloroprene, natural rubber, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, styrene-isoprene copolymer, polystyrene, styrene-acrylonitrile copolymer, ethylene-propylene copolymer, ethylene-propylene diene terpolymer, polyisobutylene, isobutylene-isoprene copolymer, poly-methylacrylate, polyethylacrylate, polyyropylacrylate, polybutylacrylate, polymethyl methacrylate, ethylene-vinylacetate copolymer, polycarbonate, yolyethylene, polypropylene, polyvinylchloride and cellulose esters; and the grafting monomer of the graft copolymer (B) being identical to or compatible with the monomer of rubber (A) and being at least one monomer selected from butadiene, isoprene, chloroprene, isobutylene, butadiene/styrene, butadiene/
acrylonitrile, isoprene/styrene, isoprene/isobutylene, methylacrylate, ethyl-acrylate, propylacrylate, butylacrylate, isoprene/butadiene, chloroprene/
isoprene and isoprene/acrylonitrile.

2. A rubber mixture as claimed in claim 1, comprising 95 to 70% by weight of rubber (A) and 5 to 30% by weight of graft copolymer (B).

3. A rubber mixture as claimed in claim 1, wherein the graft monomer of graft copolymer (B) is present in an amount of 10 to 80% by weight based on the graft base.

4. A rubber mixture as claimed in claim 3, wherein the graft monomer of graft copolymer (B) is present in an amount of 30 to 60% by weight based on the graft base.

5. A rubber mixture as claimed in claim 1 wherein the rubber (A) is selected from natural rubber, polybutadiene, polyisoprene, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, isoprene-isobutylene copolymer, ethylene-propylene copolymer and polychloroprene.

6. A rubber mixture as claimed in claim 1, wherein the rubber (A) is a butadiene-acrylonitrile copolymer.

7. A rubber mixture as claimed in claim 1, wherein the graft copolymer (B) is produced from latex bases having a particle size of from 0.1 to 1.0 µ.

8. A rubber mixture as claimed in claim 1, wherein the proportion of graft copolymer is from 1 to 30%.

9. A rubber mixture as claimed in claim 1, wherein the graft base is crosslinked.

10. A rubber mixture as claimed in claim 1, wherein the polymer chains of the graft monomer have a molecular weight of from 2000 to 150,000.

11. A rubber mixture as claimed in claim 10, wherein the polymer chains of the graft monomer have a molecular weight of from 5,000 to 150,000.

12. A rubber mixture as claimed in claim 1, wherein the graft copolymer (B) is uncrosslinked.

13. A rubber mixture as claimed in claim 1, wherein the graft copolymer (B) is produced by grafting in benzene, toluene, xylene or mixtures thereof by means of radical initiators.

14. A rubber mixture as claimed in claim 1, wherein the graft copolymer (B) is produced in one or more aliphatic solvents by means of radical initiators.

15. A rubber mixture as claimed in claim 14, wherein the aliphatic solvent is hexane, pentane, cyclohexane, or mixtures thereof.

16. A rubber mixture as claimed in claim 1, wherein the graft copolymer (B) is produced in mixtures of aliphatic and aromatic solvents by means of radical initiators.