without wishing to be bound by theory , applicant believes the thermoplastic part of the graft polymer acts as a labile thermoplastic cross - linking agent . it is believed that if the tackifier resin were soluble in the thermoplastic , it would not provide so great an improvement in the adhesive properties . in a preferred aspect of the present invention the elastomer comprises : at least 85 weight percent of one or more monomers selected from the group consisting of isoprene and chloroprene , mosts preferably isoprene ; up to 15 weight percent of a monomer selected from the group consisting of c 1 - 8 alkyl or hydroxyalkyl esters of a c 3 - 8 ethylenically unsaturated carboxylic acid and up to 5 , preferably 1 to 25 , weight percent of one or more monomers selected from the group consisting of : ( i ) c 3 - 6 ethylenically unsaturated carboxylic acids ; ( ii ) c 3 - 6 ethylenically unsaturated aldehydes ; and ( iii ) amides of c 3 - 6 ethylenically unsaturated carboxylic acids , which amides may be unsubstituted or substituted at the nitrogen atom by up to two radicals selected from the group consisting of c 1 - 4 alkyl and hydroxyalkyl radicals . suitable c 3 - 6 ethylenically unsaturated acids comprise acrylic acid , methacrylic acid , itaconic acid and fumaric acid . acrolein is included in suitable c 3 - 6 ethylenically unsaturated aldehydes . useful c 2 - 8 alkyl and hydroxyalkyl esters of c 3 - 6 ethylenically unsaturated carboxylic acids include ethyl butyl , hydroxyethyl , and ethylhexyl acrylate and methacrylate . useful amides of c 3 - 6 ethylenically unsaturated carboxylic acids include acrylamide , methacrylamide and n - methyhol acrylamide . most preferably , the elastomer comprises at least 95 weight percent of isoprene and up to 5 weight percent of one or more monomers selected from the group consisting of acrylic acid , methacrylic acid , itaconic acid and fumaric acid . the elastomer should be such that from 40 to 80 , preferably 50 to 70 percent of the elastomer is soluble in tetrahydrofuran ( thf ). the median molecular weight of the portion of the elastomer soluble in thf should be from 10 3 to 10 5 most preferably from 10 4 to 10 4 . 7 . the methods for determining molecular weight are well known in the art . the preferred method is to measure the time it takes for a solution of polymer in thf or some other suitable solvent to pass through a chromatographic column . the methods of controlling the molecular weight distribution of an emulsion polymer are also well known as discussed in u . s . pat . nos . 4 , 508 , 864 and 4 , 540 , 739 assigned to polysar limited , the disclosures of which are hereby incorporated by reference . the elastomer should have a tg of less than - 30 ° c ., preferably from - 80 ° to - 35 ° c . the thermoplastic must be thermodynamically incompatible with the elastomer . this means that the elastomer and the thermoplastic will tend to be , and most preferably are , separate phases . the thermoplastic graft portion of the polymer is a polymer having a tg from 35 to 120 , preferably from 50 ° to 110 ° c . the thermoplastic polymer may be a co - or homo polymer of one or more monomers from the group consisting of c 8 - 12 vinyl or vinyldene aromatic monomers which may be unsubstituted or substituted by a c 1 - 4 alkyl radical , c 1 - 2 alkyl acrylates and c 1 - 2 alkyl methacrylates . polystyrene is a particularly useful thermoplastic . the ratio of graft thermoplastic to elastomer may range from 30 : 70 to 5 : 95 . most preferably the thermoplastic : elastomer ratio is from 20 : 80 to 10 : 90 . in addition to the latex of the graft polymer , the adhesive compositions of the present invention comprise a tackifier resin . the tackifier should be more soluble in the elastomeric part of the polymer and less soluble in the thermoplastic part of the polymer . suitable tackifiers include those produced from the c 5 cut of a stream of aliphatic hydrocarbons . such tackifiers include terpene resins , pinene resins , piperylene , and isoprene tackifiers . the tackifier may be present in an amount from 20 to 250 , preferably 50 to 150 parts by weight per 100 parts by weight of polymer . the tackifier resin may be added to the latex as an aqueous dispersion or emulsion , or it may be added as a melt . preferably , it is added as an aqueous dispersion . the adhesives of the present invention are particularly useful in pressure sensitive adhesives . generally , the adhesive is applied to a substrate at a dry coat weight from 6 to 68 . 0 gm / m 2 ( 0 . 2 to 2 oz / yd 2 ). ( the web or sheet is then slit or punched to the required width and / or dimension .) the substrate may be a woven or non woven web or sheet , an extruded sheet , or a foil . the woven or non woven may be made from natural cellulose fiber such as cotton , jute , etc . or a natural amide ( protein ) type fiber such as wool . the woven or non woven may be made from synthetic fibers such as polyester , polyamide or aramide fibers . the substrate may be a thin metal foil such as aluminum . the web may be an extruded sheet up to about 1 / 8 &# 34 ; thick of a polyolefin such as ethylene or propylene or a polymer such as poly vinyl chloride , polyvinylidene chloride or polyterephthalate resin . the web may be a non woven web saturated with a polymeric binder such as a styrene butadiene type or an acrylic type of polymer . this is particularly useful where it is desired to prevent the tackifier from diffusing down into the web , as may occur in masking tape or lables if the tackifier is soluble in the polymer which binds the base web . suitable fibers for the non woven web include cellulosefibers , which may be untreated , such as wood pulp or regenerated cellulose such as rayon , polyesters , poly acrylates , poly amides such as nylon and the like . the following examples are intended to illustrate the invention and not to limit it . in the examples unless otherwise specified , the parts are parts by dry weight . the latices were tackified with an emulsion of a polyterpene resin ( beta pinene ) sold under the trademark piccolyte s - 90 . the amount of tackifer and polymer are indicated in the table . the resulting adhesive was drawn down on a mylar ( trademark ) film at a dry coat weight of 25 g / m 2 ( 0 . 7 oz / yd 2 ) and the films were dried at 115 ° c . for 3 minutes resulting in a psa coating 25 microns thick . the resulting adhesive were then tested using standard pressure sensitive tape council ( pstc ) tests ( 7th edition ). the results are set forth in table i . table i__________________________________________________________________________ polymer type a b c d e f g hparts ( dry wt .) 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100__________________________________________________________________________piccolyte 100 120 150 0 40 80 120 0 30 70 0 50 50 50 50 50s - 90 ( parts dry wt . ) 180 ° peel 328 475 606 461 556 623 496 247 114 119 116 614 537 485 564 452 ( stainless steel ) gm cm . sup .- 190 ° quick stick 245 319 415 247 91 67 12 92 28 23 175 704 313 440 341 434 ( stainless steel ) gm cm . sup .- 1shear adhesion 40 43 81 136 36 44 99 18 . 3 70 243 0 . 1 3 . 0 7 . 5 137 . 8 121 137 . 82 . 5 m × 1 . 25 mhours__________________________________________________________________________ ( 1 ) the desire to improve the shear of natural rubber / tackifier blends ( col . a ). ( 2 ) the desire to improve the shear of carboxylated poly isoprene / tackifier blends ( col . d ). ( 3 ) random polymers of styrene , isoprene and itaconic acid gives excellent shear but inadequate tack properties ( col . b ) ( 4 ) random polymers of acylonitrile and isoprene share good shear properties , but inadequate tack properties ( col . c ). ( 5 ) the polyisoprene grafted with 10 percent styrene may be compounded with tackifiers to obtain acceptable tack and shear properties .