char promoters and hydration water sources the neoprene itself can be a homopolymer of chloroprene or a copolymer or chloroprene with another organic monomer usual monomers are vinyl compounds or olefinic compounds such as for example styrene a vinyltoluene a vinylnaphthalene 1 3 butadiene isoprene 2 3 dimethyl 1 3 butadiene 2 3 dichloro 1 3 butadiene methyl vinyl ether vinyl acetate methyl vinyl ketone ethyl acrylate methyl methacrylate methacrylamide and acrylonitrile the proportion of the organic monomer other than chloroprene can be up to about 60 of the total polymer but usually less than 20 the preferred monomer is acrylonitrile or an u03b1 u03b2 unsaturated carboxylic acid for example acrylic acid or methacrylic acid the preferred proportion of acrylonitrile or the carboxylic acid monomer is such that that proportion of the copolymer weight which is contributed by the nitrile or carboxyl groups cooh is about 2 20 in the case of carboxyl groups the usual proportion would be about 5 or less it has been surprisingly found that copolymers of chloroprene and acrylonitrile or an u03b1 u03b2 unsaturated carboxylic acid form under cigarette test conditions a char having good structural integrity so that other char promoters either are not required or can be used in small amounts only the neoprene polymer is prepared by any well known technique but usually by emulsion polymerization in the presence of a free radical initiator such as an organic peroxide or hydroperoxide a chain transfer agent such as an alkyl mercaptan or a dialkyl xanthogen disulfide also is present chloroprene polymerization techniques are described in detail in the following.