Abstract
Free radical copolymerization of chloroprene (Cp) with elemental sulphur (S 8) was studied in a range of temperatures from 20 to 100°C as a function of total monomer concentration. The sulphur rank distribution for the sulphur unit S x , where 2⩽ x⩽8, has been examined by observing proton nuclear magnetic resonance spectra of the methylene group directly bonded to sulphur. The effect of total monomer concentration and polymerization temperature on the copolymer structure is explained by the depropagation process involving both carbon-sulphur and sulphur-sulphur bond scissions. It was found that the population of polysulphide linkages shorter than octasulphide, such as S 2 and S 3, increases with dilution or with increasing polymerization temperature. Disulphide linkages were favourably formed at rather low temperatures with dilution; other polysulphide linkages such as S 3 became more favourable at higher temperatures. The back-biting mechanism, in which a propagating radical of a terminal Cp unit attacks a penultimate sulphur unit, is proposed for the depropagation process to explain the sulphur rank distribution.
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