Anionic Polymerization of Acrylates. Synthesis of (Meth)acrylate Di- and Triblock Copolymers Using the Li Ester−Enolate/tert-Alkoxide Initiating System

Abstract

Methacrylate di- and triblock copolymers composed of methyl (MMA), butyl (BuMA), 2-(dimethylamino)ethyl (DMAMA), and 2-ethylhexyl (EtHMA) methacrylates and tert-butyl acrylate (t-BuA) blocks were prepared by ligated anionic polymerization and characterized by SEC and NMR. The process was initiated with the system methyl 2-lithioisobutyrate/lithium tert-butoxide (MIB-Li/t-BuOLi) at the 1/10 mole ratio, which was recently described as the optimum composition, at THF at -60 °C. The monomers were added to the reaction mixture successively after chosen polymerization intervals and products of the individual polymerization steps were isolated and analyzed. Molecular weights of methacrylate copolymers increased with increasing total amount of the monomers added, and the products of the two-or three-step polymerizations were not detectably contaminated with the products of the foregoing steps, so that the corresponding MWD curves were unimodal and symmetric. The product of MAIA/t-BuA block copolymerization exhibited bimodal MWD, originating probably by the self-termination proceeding at the beginning of the second polymerization step after addition of an acrylate monomer to the living polymethacrylate. A possible mechanism of self-termination and reactions of polymethacrylate chains bearing a few terminal acrylate units are briefly discussed.