crotonic acid vinylidene chloride a vinyl alkyl ether for example vinyl ethyl ether etc an ester of maleic acid n vinyl 2 pyrrolidone n vinylpyridine 2 or 4 vinylpyridine etc of these monomers an ester of acrylic acid an ester of methacrylic acid and styrene and styrene derivatives are particularly preferred two or more ethylenic unsaturated monomers can be used together for example a combination of methyl acrylate and butyl acrylate ethyl acrylate and styrene tetrahydrofuryl methacrylate and ethylacrylate methyl acrylate and ethyl acrylate etc can be used the polymeric latex used in the invention can be prepared by emulsion polymerization or solution polymerization technique emulsion polymerization is preferred emulsion polymerization is well known in the art and is described for example in f a bovey emulsion polymerization issued by interscience publishers inc new york 1955 examples of the chemical initiators which may be used include a thermally decomposable initiator for example a persulfate such as ammonium persulfate potassium persulfate sodium persulfate hydrogen peroxide 4 4 u2032 azobis 4 cyanovaleric acid and redox initiators such as hydrogen peroxide iron ii salt potassium persulfate sodium hydrogensulfate potassium persulfate sodium metabisulfite potassium persulfate sodium hydrogen bisulfite cerium salt alcohol etc emulsifiers which may be used in the emulsion polymerization include soap a sulfonate for example sodium n methyl n oleoyltaurate sodium dodecylbenzene sulfonate alpha olefin sulfonate diphenyloxide disulfonate naphthalene sulfonate sulfosuccinates and sulfosuccinamates polyether sulfonate alkyl polyether sulfonate alkylarylpolyether sulfonate etc a sulfate for example sodium dodecyl sulfate a phosphate for example nonylphenol ethoxylate phosphate linear alcohol alkoxylate phosphate alkylphenol ethoxylate phosphate phenol ethoxylate a cationic compound for example cetyl trimethylammonium bromide hexadecyl trimethylammonium bromide etc an amphoteric compound and a high molecular weight protective colloid for example polyvinyl alcohol polyacrylic acid gelatin etc a second class of polymeric lattices used.