Abstract:

Controlled/living polymerization kinetics of vinyl acetate(VAc) was studied. Poly(vinyl acetate)(PVAc) with predetermined molecular mass and relatively low polydispersity was successfully synthesized from vinyl acetate(VAc) by a degenerative transfer radical polymerization with the presence of iodine（0.57%～0.86% mass fraction of the system） using 2,2′-azobis(isobutyronitrile)(AIBN) as the initiator. The effects of iodine concentration on reaction speed and relative molecular mass and relatively polydispersity were investigated. The results indicated that the increasing speed of molecular mass was successfully controlled and relatively polydispersity was narrowed with increasing iodine concentration. The polymerization was monitored by an on-line 1H NMR spectroscopy to investigate the evolution of several compounds in the reaction medium, especially the adduct between primary radicals and iodine(A-I, where A stands for the radical fragment from the initiator), and the monoadduct A-Mn-I(where M stands for the monomer unit). The structure of the poly(vinyl acetate) iodo-terminated chain end groups by this method was proved using 1H NMR spectrum. Molecular masses increase linearly with conversion and molecular polydispersities decrease gradually with improving monomer conversion of vinyl acetate, and polymers with relatively narrow molecular polydispersities(Mw/Mn≤1.41) are obtained when the monomer conversion of vinyl acetate reaches up to 80%, indicating that the process of degenerative transfer polymerization efficiently controls the number-average molecular mass and molecular polydispersities in the presence of molecular iodine(I2), therefore the process is a controlled/living radical polymerization.

Key words: poly(vinyl acetate), iodine, degenerative transfer polymerization, living radical polymerization, vinyl acetate.