ACRYLONITRILE COPOLYMERS WHICH HAVE HIGH RECEPTIVITY TO ACID DYES AND ARE FLAME RESISTANT, AND ARE THUS USEFUL IN MAKING CARPETING, CURTAINS, ETC. AS WELL AS WEARING APPEREL, ETC., ARE TERNARY POLYMERS COMPOSED OF ACRYLONITRILE, VINYLIDENE CHLORIDE, AND A BASIC MONOMER OF THE TYPE OF THE DIMETHYLAMINOETHYL AND DIETHYLAMINOETHYL ESTERS OF ACRYLIC ACID AND OF METHACRYLIC ACID, AND THE CORRESPONDING N-SUBSTITUTED AMINOPROPL AND AMINOBUTYL ESTERS, ETC.; OR COPOLYMERS CONSISTING OF ACRYLONITRILE, VINYLIDENE CHLORIDE, A BASIC MONOMER OF THE AFORE-INDICATED TYPE AND ONE OR MORE NEUTRAL ETHYLENCIALLY UNSATURATED COMPOUNDS (I.E. METHYL ACRYLATE, METHYL METHACRYLATE, VINYL ACETAT, STYRENE).