Block copolymers of poly(ε-caprolactone) with ph-responsive side-chain amino acid moieties.

Abstract

To prepare amphiphilic block copolymers consisting of biocompatible and biodegradable segments, herein we report synthesis of diblock copolymers having ε-caprolactone (ε-CL) repeating units in one block and amino acid-based acrylate monomers in another segment. The block copolymers were prepared by a combination of metal-free ring-opening polymerization (ROP) of ε-CL and reversible addition-fragmentation chain transfer (RAFT) polymerization of tert-butyloxycarbonyl (Boc)-alanine/Boc-leucine based acrylate monomers. The ROP of ε-CL was initiated with diphenyl phosphate (DPP) as a metal-free catalyst in conjunction with a heterofunctional initiator, benzyl-2-hydroxyethyl carbonotrithioate, produced trithiocarbonate terminated poly(ε-caprolactone) (PCL). This was further employed as macro-chain transfer agent for the synthesis of side chain amino acid containing block via RAFT. Deprotection of Boc group pendants from the block copolymers under acidic conditions at room temperature provided pH responsive block copolymers with positively charged cationic primary amine functionalities. Furthermore, self-assembling nature of these block copolymers in aqueous medium was examined through dynamic light scattering (DLS) and field emission-scanning electron microscopy (FE-SEM).