Synthetic rubber-like materials of improved resistance to oil and freezing are prepared by copolymerizing a mixture of from 80-97 per cent of 2 - fluoro - 1.3 - butadiene or a homologue thereof, and from 20-3 per cent of acrylonitrile or alkyl-substituted acrylonitriles. Preferably, the copolymerization is carried out in aqueous emulsion containing a peroxide or persulphate catalyst. The resulting latex may be stabilized before coagulation and the copolymer compounded, molded and vulcanized by processes usual to chloroprene synthetic rubbers. In examples, fluoroprene and acrylonitrile are emulsified in an aqueous medium containing sodium oleate, sodium hydroxide, a formaldehyde/sodium naphthalene sulphonate condensation product, potassium persulphate, potassium ferricyanide and lauryl mercaptan and copolymerized in a sealed vessel under heat and agitation. After stabilization and coagulation the product may be compounded and cured. Specifications 504,466 and 570,662 are referred to.