Free‐radical retrograde‐precipitation copolymerization of vinyl acetate and acrylic acid

Abstract

Free-radical chain polymerization kinetics of vinyl acetate (VA) and acrylic acid (AA) exhibit some unusual control features. The VA radicals have a high rate of chain transfer leading to relatively sluggish propagation rates. Polymerization of AA, however, is prone to autoacceleration behavior in bulk, solution, and precipitating media. Thus, conventional statistical copolymerization of VA and AA would result in the preferential formation of high AA content copolymer. However, when the reaction medium is chosen in such a way that the copolymer precipitates above the lower critical solution temperature (LCST), propagation control and even monomer sequence control are obtained. Under these conditions, when the VA charge is much greater than AA, a tapered block copolymer (VA-t-AA) is obtained. We report a single stage polymerization process for the synthesis of such materials. The presence of VA-t-AA products is verified by emulsification, solubility, fractionation, size exclusion chromatography, NMR, and thermal analyses. In addition, propagation control can virtually eliminate formation of bimodal MWD and random/ homopolymer materials that are associated with various chain transfer mechanisms in conventional polymerization routes.

Kinetic study of RuIII -catalyzed polymerization of methylmethacrylate initiated with n -butylamine in the presence of carbon tetrachloride by a charge-transfer mechanism

“…The acceleration of the rate of polymerization of some monomers by Pd II has been observed [12,13]. Polymerization of methylmethacrylate (MMA) initiated by amines in the presence of CCl 4 by a charge-transfer mechanism [14][15][16][17][18][19][20][21][22][23][24][25], amines, and Ru III complexes is also a very effective system in atom transfer radical polymerization mechanism [26,27], and a free-radical retrograde-precipitation polymer mechanism has been studied widely by many investigators [28][29][30][31][32][33][34][35]. It has been observed that two different mechanisms [36,37] for the initiation of polymerization of MMA, involving the charge-transfer complex formed by the interaction of amine and CCl 4 -under the conditions [CCl 4 /amine]≤1-and by the interaction of amine and MMA-under the conditions [CCl 4 /amine]≥1 have been proposed.…”