Polyisobutylene-Based Helical Block Copolymers with pH-Responsive Cationic Side-Chain Amino Acid Moieties by Tandem Living Polymerizations

Syntheses of diblock copolymers of isobutylene (IB) with amino acid-based monomers were carried out by a combination of living carbocationic and reversible addition–fragmentation chain transfer (RAFT) polymerizations. Cationic polymerization of IB followed by hydroboration oxidation produced hydroxyl end-capped polyisobutylene, which was subsequently converted into macro-chain-transfer agent (macro-CTA) for the RAFT polymerization of tert-butyloxycarbonyl (Boc)-protected amino acid-based monomers such as Boc-l-alanine methacryloyloxyethyl ester (Boc-l-Ala-HEMA) and Boc-l-leucine methacryloyloxyethyl ester (Boc-l-Leu-HEMA). The block length and molecular weight could be controlled while maintaining a narrow molecular weight distribution. These block copolymers form core–shell type micellar structure in methanol—a good solvent for side-chain amino acid block but bad solvent for polyisobutylene segment. Specific rotation and circular dichroism (CD) studies indicated the chiral nature of the block copolymers ...