Synthesis of poly(l-lactide)-b-poly(amino acid) block copolymers by noncovalent protection of hetero-initiators†

Abstract

The synthesis of poly(l-lactide)-b-poly(amino acid) (PLA-b-PAA) block copolymers is of great interest in biomedicine due to their pronounced biodegradability and biocompatibility. However, the traditional method for preparing the functional block copolymers generally involves a tedious protection and deprotection process by covalent bonding, which may not only degrade the PLA segment during the process but also eliminate the precision in controlling the ROP of NCA. In light of this, in this study, PLA-b-PAAs were directly synthesized by the noncovalent protection between triethylborane (Et₃B) and an amino alcohol initiator during the ring-opening polymerization (ROP) process of LA under mild reaction conditions, which produced amino-terminated PLA (PLA-NH₂) avoiding the tedious process of the traditional method. Subsequently, the PLA-NH₂ macroinitiator was employed to initiate the ROP of N-carboxyanhydride, thereby forming the well-defined PLA-b-PAA block copolymers. The noncovalent protection of hetero-initiators provides a promising platform for the design of PLA-b-PAA polymeric materials with tailored functionalities for biomedical applications.