in the above formula , r is a saturated aliphatic or aromatic group having 1 to 10 carbon atoms and preferably 1 to 6 carbon atoms . examples of suitable r groups are methyl , ethyl , propyl , isopropyl , butyl , isobutyl , benzyl , phenyl , tolyl , xylyl , phenethyl , and naphthyl . the alkyl groups are preferred . the subscript a is preferably in the range of about 8 to about 200 , and the subscript b is preferably in the range of about 8 to about 30 . the linear organopolysiloxane / alpha - olefin copolymer of the invention is prepared by reacting an organopolysiloxane having the following formula : ## str3 ## wherein r and a are as above with an alpha - olefin having the following formula : wherein b is as above . the alpha - olefins are exemplified by 1 - hexene , 1 - octene , 1 - dodecene , 1 - tetradecene , 1 - hexadecene , 1 - octadecene , 1 - eicosene , 1 - doeicosene , 1 - tetraeicosene , 1 - hexaeicosene , 1 - octaeicosene , 1 - triacontene , 1 - dotriacontene , 1 - tetratriacontene , 1 - hexatriacontene , 1 octatriacontene , 1 - tetracontene , 1 - pentacontene , 1 - hexacontene , 1 - heptacontene , 1 - octacontene , 1 - nonacontene , and 1 - decacontene . these alpha - olefins can be used individually or as a mixture . the reaction of the siloxane and alpha - olefin is carried out in the presence of a hydrosilylation catalyst . the catalyst can be an organic peroxide , an azo compound , a platinum compound such as chloroplatinic acid , or a platinum compound or platinum supported on an inert carrier such as silica or alumina . a preferred catalyst is an oxidated platinum acid , either in a unsupported or supported state . platinum acid chloride is an example . platinum hydrocarbon complexes and platinum alcoholate are also useful as catalysts a solvent is used where one of the reactants does not dissolve in the other reactant . a suitable solvent will be inert to the reaction , examples being benzene , toluene , hexene , pentane , hexane , heptane , octane , cyclopentane , cyclohexane , methanol , ethanol , propanol , and butanol . the reaction can be carried out at a temperature in the range of about 50 ° c . to about 150 ° c . and is preferably effected at a temperature in the range of about 80 ° c . to about 120 ° c . there is no requirement as to pressure , i . e ., the reaction can be carried out at subatmospheric , atmospheric , and superatmospheric pressures . generally , the orqanopolysiloxane , one or more alpha - olefins , the catalyst , and an inert solvent are introduced into a reactor under an inert atmosphere such as nitrogen . the reaction is continued until the viscosity of the mixture stops increasing . the reaction product is then neutralized and purified to provide the linear organopolysiloxane / alpha - olefin copolymer of the invention . for each 100 parts of organopolysiloxane in the reaction mixture , the other components are added about as follows : ______________________________________ parts by weightcomponent broad range preferred range______________________________________alpha - olefin 10 to 60 20 to 40catalyst 0 . 001 to 0 . 01 0 . 003 to 0 . 005solvent ( if needed ) 0 to 50 10 to 30______________________________________ in order to utilize the linear organopolysiloxane / alpha - olefin copolymer in the manufacture of film , sheet , or tubing , the copolymer can be mixed with a crosslinkable thermoplastic resin , an aliphatic compound having two or more carbon to carbon double bonds , preferably two double bonds , and an organic peroxide crosslinking agent . the thermoplastic resin can be any cross - linkable homopolymer or copolymer produced from two or more comonomers , or a blend of two or more of these polymers , conventionally used in film , sheet and tubing , and as jacketing and / or insulating materials in wire and cable applications . generally , the monomers useful in the production of these homopolymers and copolymers will have 2 to 20 carbon atoms . examples of such monomers are alpha - olefins such as ethylene , propylene , 1 - butene , 1 - hexene , 4 - methyl - 1 - pentene , and 1 - octene ; unsaturated esters such as vinyl acetate , ethyl acrylate , methyl acrylate , methyl methacrylate , t - butyl acrylate , n - butyl acrylate , n - butyl methacrylate , 2 - ethlyhexyl acrylate , and other alkyl acrylates ; diolefins such as 1 , 4 - pentadiene , 1 , 3 - hexadiene , 1 , 5 - hexadiene , 1 , 4 - octadiene , and ethylidene norbornene ; other monomers such as styrene , p - methyl styrene , alpha - methyl styrene , p - chloro styrene , vinyl naphthalene , and similar aryl olefins ; nitriles such as acrylonitrile , methacrylonitrile , and alpha - chloroacrylonitrile ; vinyl methyl ketone , vinyl methyl ether , vinylidene chloride , maleic anhydride , vinyl chloride , vinyl alcohol vinylidene chloride , tetrafluoroethylene , and chlorotrifluoroethylene ; and acrylic acid , methacrylic acid , and other similar unsaturated acids . the homopolymers and copolymers referred to can be non - halogenated , or halogenated in a conventional manner , generally with chlorine or bromine . examples of halogenated polymers are polyvinyl chloride , polyvinylidene chloride , and polytetrafluoroethylene . in addition to polyolefins , included among the polymers can be polyesters , polycarbonates , and polyurethanes . the homopolymers and copolymers of ethylene are preferred , both in the non - halogenated and halogenated form . included in the preferred group are terpolymers such as ethylene / propylene / diene monomer rubbers . aliphatic compounds having two double bonds are exemplified by the following compounds : 1 , 5 hexadiene , 1 , 6 heptadiene , 1 , 7 octadiene , 1 , 8 nonadiene , 1 , 9 decadiene , 1 , 10 undecadiene , 1 , 11 dodecadiene , 1 , 12 tridecadiene , 1 , 13 tetradecadiene , 1 , 14 pentadecadiene , 1 , 15 hexadecadiene , 1 , 16 heptadecadiene , 1 , 17 octadecadiene , bis ( 4 - acryloxy polyethoxy phenyl ) propane , 1 , 3 butylene glycol diacrylate , pentanediol diacrylate , neopentyl glycol diacrylate , 1 , 6 hexanediol diacrylate , diethylene glycol diacrylate , triethylene glycol diacrylate , tetraethylene glycol diacrylate , trimethylol propane triacylate , ethylene glycol dimethacrylate , 1 , 4 butanediol diacrylate , 1 , 3 butylene glycol dimethyacrylate , neopenthyl glycol dimethacrylate , 1 , 6 hexanediol dimethacrylate , diethylene glycol dimethyacrylate , triethylene glycol dimethacrylate , dipropylene glycol dimethacrylate , trimethylol ethane trimethacrylate , trimethylol propane trimethacrylate , diacryl phthalate , triallyl cyanurate , triallyl isocyanurate , triallyl trimellitate , and diallyl cholendate . the organic peroxide crosslinking agent used in the composition of this invention preferably has a decomposition temperature of 100 ° to 220 ° c . for a half - life of 10 minutes and is exemplified by the following compounds ( the numbers set off by the parentheses are their decomposition temperatures (° c . )): succinic acid peroxide ( 110 ), benzoyl peroxide ( 110 ), t - butyl peroxy - 2 - ethyl hexanoate ( 113 ), p - chlorobenzoyl peroxide ( 115 ), t - butyl peroxy isobutylate ( 115 ), t - butyl peroxy isopropyl carbonate ( 135 ), t - butyl peroxy laurate ( 140 ), 2 , 5 - dimethyl - 2 , 5 - di ( benzoyl peroxy ) hexane ( 140 ), t - butyl peroxy acetate ( 140 ), di - t - butyl diperoxy phthalate ( 140 ), t - butyl peroxy maleic acid ( 140 ), cyclohexanone peroxide ( 145 ), t - butyl peroxy benzoate ( 145 ), dicumyl peroxide ( 150 ), 2 , 5 - dimethyl - 2 , 5 - di ( t - butyl peroxy ) hexane ( 155 ), t - butyl cumyl peroxide ( 155 ), t - butyl hydroperoxide ( 158 ), di - t - butyl peroxide ( 160 ), 2 , 5 - dimethyl - 2 , 5 - di ( t - butyl peroxy ) hexane - 3 ( 170 ), di - isopropyl benzene hydroperoxide ( 170 ), p - menthane hydroperoxide ( 180 ), and 2 , 5 - dimethyl hexane - 2 , 5 - dihydroperoxide ( 213 ). in these compositions , which can be formed using conventional techniques such as extrusion , injection molding , calendering , and compression molding , for each 100 parts by weight of crosslinkable thermoplastic resin , suitable amounts of other components can be about as follows : ______________________________________ parts by weightcomponent broad range preferred range______________________________________organopolysiloxane / 0 . 01 to 300 0 . 05 to 60olefin copolymerunsaturated aliphatic 0 . 01 to 10 0 . 1 to 2compoundorganic peroxide 0 . 1 to 10 0 . 5 to 3crosslinking agent______________________________________ these components can be used individually or mixtures of two or more of each of these components can be used . useful additives for the above composition are coupling agents , surfactants , reinforcing filler or polymer additives , antioxidants , ultraviolet stabilizers , antistatic agents , pigments , dyes , slip agents , plasticizers , lubricants , viscosity control agents , extender oils , metal deactivators , water tree growth retardants , voltage stabilizers , flame retardant additives , and smoke suppressants . subject composition is usually heat - kneaded to make it homogeneous and prepare it for forming , i e ., for extruding or molding , into film , sheets , tubes , and other articles of manufacture . the heat - kneading can be conducted in a banbury mixer , a twin screw extruder , or in other conventional kneading apparatus . the kneading temperature is preferably in the range of about 100 ° to about 300 ° c . the forming equipment is also conventional . a linear organopolysiloxane / alpha - olefin copolymer as described above is prepared by reacting 100 parts by weight of an organopolysiloxane having the formula : ## str4 ## with 30 parts by weight of a mixture of alpha - olefins ( c 20 , c 22 , c 24 , c 26 and c 28 ) in the presence of platinum acid chloride at 25 ° c . it is noted that the resultant copolymer is waxy . the copolymer is incorporated into the following composition . 100 parts by weight of ethylene / vinyl acetate copolymer having a melt index of 2 . 5 grams per 10 minutes and containing 18 percent by weight vinyl acetate ( based on the weight of the copolymer ); 40 parts by weight of the above prepared organopolysiloxane / alpha - olefin copolymer ; 1 part by weight triallyl trimellitate ; 2 parts by weight dicumyl peroxide ; and 0 . 1 part by weight of an antioxidant , tetrakis [ methylene ( 3 , 5 - di - tert - butyl - 4 - hydroxyhydrocinnamate )] methane are kneaded at 160 ° c . for 20 minutes in a brabender mixer . the mixture is then compression formed into a 1 millimeter thick sheet . the sheet has a melt index of 30 grams per 10 minutes ; a tensile strength of 80 kilograms per square centimeter ; an elongation of 350 percent ; and exhibits substantially no blooming . the sheet is pelletized and extruded into a tape at 160 ° c . example 1 is repeated without the dicumyl peroxide ; however , the kneader slipped and a homogeneous product could not be formed . example 1 is repeated except that the orqanopolysiloxane has the following formula : ## str5 ## the alpha - olefin is a mixture of alpha - olefins , each having 30 or more carbon atoms ; the crosslinkable thermoplastic resin is an ethylene / ethyl acrylate copolymer having a melt index of 6 grams per 10 minutes and containing 18 percent by weight ethyl acrylate ; 30 parts by weight of the organopolysiloxane / alpha - olefin copolymer are used ; the unsaturated aliphatic compound is triallyl isocyanurate ; and kneading is carried out for 30 minutes . the results differ for this sheet in that the melt index is 40 grams per 10 minutes ; the tensile strength is 60 kilograms per square centimeter ; and the elongation is 300 percent . example 1 is repeated except that the crosslinkable thermoplastic resin is an ethylene - 1 - butene copolymer having a melt index of 4 . 7 grams per 10 minutes and a density of 0 . 900 gram per cubic centimeter ; 35 parts by weight of the organopolysiloxane / alpha - olefin copolymer are used ; 2 parts by weight of the unsaturated aliphatic compound , in this case , triallyl isocyanurate , are also used ; and kneading is carried out at 100 ° c . for 10 minutes and then at 160 ° c . for 10 minutes . the results differ in that the melt index is 30 grams per 10 minutes ; the tensile strength is 120 kilograms per square centimeter ; and the elongation is 600 percent . example 1 is repeated except that the pellets are formed into a 70 micron thick inflated film at an extrusion temperature of 170 ° c . and a blow ratio of 1 : 6 using a 40 millimeter screw extruder having a length to diameter ratio of 24 ; and the inflated film has a rupture strength of about 220 kilograms per square centimeter . example 3 is repeated except that 7 parts by weight of a mixture of c 6 , c 8 , and c 10 alpha - olefins are used ; the unsaturated aliphatic compound is triacryl isocyanurate ; and the pellets are formed at 190 ° c . into a 10 millimeter outer diameter and a 2 millimeter thick tube using a 10 millimeter diameter extruder having a length to diameter ratio of 24 and the tube has a rupture strength of about 80 kilograms per square centimeter .