Abstract
AbstractFree‐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. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
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