New chain transfer agents for free radical polymerizations

Abstract

Abstract The palmitoyl ester of N ‐hydroxypyridine‐2‐thione displayed useful chain transfer properties in free radical polymerizations of methyl methacrylate and styrene. Retardation, however, accompanied the lowering of molecular weight in methyl acrylate and vinyl acetate polymerizations. 4‐Methyl‐3‐palmitoyloxythiazol‐2(3H)‐thione had good chain transfer activity with methyl methacrylate, styrene and methyl acrylate. Although benzyl thionobenzoate exhibited virtually ‘ideal’ behaviour (chain transfer constant C x ∼1) in styrene and methyl acrylate polymerizations, it was ineffective in lowering molecular weight of poly(methyl methacrylate). Severe retardation was observed with vinyl acetate. Addition‐fragmentation pathways are postulated for chain transfer.