عنوان مقاله [English]
Homopolymerization and copolymerization of vinyl acetate (VAc) and dibutyl maleate (DBM) were performed in bulk in the presence of iodine as a chain azobis(isobutyronitrile) (AIBN) as an transfer agent generator and 2,2
initiator at 70°C. This process, known as "reverse iodine transfer polymerization" (RITP), is based on direct reaction of radicals with molecular iodine. Depending on the mole fraction of comonomers in the initial feed, P(VAc-alt-DBM)-b-PVAc block terpolymer or P(VAc-alt-DBM) alternating copolymer was synthesized. GPC and 1H NMR results showed that VAc/DBM copolymerization proceeds by controlled characteristics, i.e. with a predictable molecular weight and relatively narrow molecular weight distribution (for example, Mn = 19330 g/mol and PDI = 1.25).
These results also demonstrated the existence of two different stages. During the first stage (inhibition period), iodine was consumed to form very short ω-iodotelomers, and in the second stage, polymerization followed the kinetics of conventional free radical polymerization governed by degenerative chain transfer. In comparison with
the iodine transfer radical polymerization (ITP), reaction time of RITP of VAc and DBM, under the same conditions, was reduced to about one-fourth while the molecular weight of the produced copolymer increased significantly. Presence of DBM in the reaction mixture resulted in lower copolymerization rate and higher polydispersity index of the polymer. This may be attributed to DBM bulky side groups which can reduce addition rate of comonomers into the growing chains. Individual conversions of the comonomers were theoretically calculated by using reactivity ratios of VAc and DBM which showed a good agreement with the experimental values.