Combination of nitroxide-mediated polymerization and SET-LRP for the synthesis of high molar mass branched and star-branched poly(n-butyl acrylate) characterized by size exclusion chromatography and rheology
Résumé
Branched and star-branched polymers were successfully synthesized by the combination of two successive controlled radical polymerization methods. A series of linear and star poly(n-butyl acrylate)-co-poly(2-(2- bromoisobutyryloxy) ethyl acrylate) statistical copolymers, P(nBA-co-BIEA) x, were first synthesized by nitroxide-mediated polymerization (NMP at T > 100 °C). The subsequent polymerization of n-butyl acrylate by single electron transfer-living radical polymerization (SET-LRP at T = 25 °C), initiated from the brominated sites of the P(nBA-co-BIEA) x copolymer, produced branched or star-branched poly(n-butyl acrylate) (PnBA). Both types of polymerizations (NMP and SET-LRP) exhibited features of a controlled polymerization with linear evolutions of logarithmic conversion versus time and number-average molar masses versus conversion for final M n superior to 80,000 g mol -1. The branched and star-branched architectures with high molar mass and low number of branches were fully characterized by size exclusion chromatography. The Mark-Houwink Sakurada relationship and the analysis of the contraction factor (g' = ([η] branched/[η] linear) M) confirmed the elaboration of complex PnBA. The zero-shear viscosities of the linear, star-shaped, branched, and star-branched polymers were compared. The modeling of the rheological properties confirmed the synthesis of the branched architectures. © 2012 Wiley Periodicals, Inc.