Glass transition temperature of allyl methacrylate-n-butyl acrylate gradient copolymers in dependence on chemical composition and molecular weight

摘要

Glass transition temperatures (T(g)s) of P(AMA-co-BA) copolymers and the corresponding homopolymers, where AMA is allyl methacrylate and BA is n-butyl acrylate, obtained by means of atom transfer radical polymerization were measured using differential scanning calorimetry. Because of the (pseudoliving) nature of this polymerization technique an increase in molecular weight (MW) is produced as the reaction progresses, which gives rise to an increase in Tgs. This increment can be adequately described by the Fox-Flory's equation in both homopolymers. However, in the spontaneous gradient copolymers of P(AMA-co-BA), the expected increase in T-g with the augment of the monomer conversion is compensated by the enrichment of BA as the polymerization reaction progresses. These opposite effects with respect to the T-g values almost balance each other, and therefore no significant influence on the MW or on conversion is found. This fact establishes that T(g)s can be used to describe the profile of these gradient copolymers, and can be theoretically determined because of its dependence on the molar fraction in the copolymer. From this dependence on chemical composition along with the experimental behavior, a prediction of the Tg variation with the MW was performed. (c) 2007 Wiley Periodicals, Inc.