Free radical polymerization of vinyl acetate in the presence of liquid polysulfides

摘要

The free radical polymerization of vinyl acetate in the presence of a liquid polysulfide H(SCH_2CH_2O-CH_2OCH_2CH_2S)_nH (thiocol) was investigated from the point of view of reaction mechanism and characterization of the resulting copolymers. It was shown that, besides the thiol end groups that were consumed very rapidly, the disulfide groups within the thiocol chain were also involved in chain transfer processes. The chain transfer constant of the thiocol S-S groups in the polymerization reaction was estimated from their rate of consumption versus the rate of monomer consumption (C_T = 0.89). The resulting copolymers, made up of randomly distributed thiocol sequences and PVAc blocks, were characterized by ~1H NMR, GPC, DSC and TGA measurements. The copolymers displayed only one glass transition each, which decreased as the PVAc block length decreased, while their thermal stability was lower than that of both thiocol and PVAc. The molecular weight of the copolymers increased with VAc conversion as a consequence of the insertion of PVAc blocks within the thiocol chain.