Isosorbide-based polymethacrylates

A new monomer, acetylated methacrylic isosorbide (AMI), was synthesized in two steps employing scandium(III) triflate as a remarkably efficacious catalyst for the tandem esterification of isosorbide with acetic anhydride and methacrylic anhydride. Analysis of the crude product mixture after acetylation indicated that functionalization occurred preferentially at the endo hydroxyl group of isosorbide (endo-acetate:exo-acetate = 4.2:1). Reaction of this mixture with methacrylic anhydride gave the corresponding isomeric mixture of AMI monomers. Poly(AMI) [PAMI] prepared by radical polymerization of the mixture of AMI regioisomers was found to have a high glass transition temperature (T_g ≈ 130 °C) and good thermal stability (T_d, 5% weight loss; N₂ = 251 °C, air = 217 °C). Reversible addition-fragmentation chain transfer (RAFT) polymerization of AMI using a new chain transfer agent, hydroxyethyl 4-cyano-4-(phenylcarbonothioylthio)pentanoate (HO-CPAD), yielded PAMI-CTA samples with controlled molar masses and narrow molar mass distributions (D ≤ 1.09). Subsequent chain extension of PAMI-CTA with n-butyl acrylate gave a series of PAMI-b-PnBA block copolymers ranging from 17-36 wt % PAMI. All samples of PAMI-b-PnBA exhibited two well-separated T_g values at approximately -45 and +120 °C, indicative of microphase separation.