Versatile synthesis of asymmetrical dendron-like/dendron-like poly(ε-caprolactone)-b-poly(γ-benzyl-L-glutamate) block copolymers

Abstract

Dendron-like/dendron-like poly(ε-caprolactone)-b-poly(γ-benzyl-L-glutamate) block copolymers with asymmetrical topology (PCL-b-PBLGn, both the subscript and the superscript denote the degree of polymerization and the branch number, respectively; n = 1, 2, and 4) were synthesized by combining ring-opening polymerization (ROP) and click chemistry. The dendron-like propargyl focal point PCL precursor with eight branches was synthesized from the controlled ROP of ε-caprolactone, and then click conjugated with azido focal point poly(amido amine) dendrons to generate the PCL-dendrons with multiple primary amine groups. The PCL-dendrons were further used as macroinitiators for the ROP of γ-benzyl-L-glutamate N-carboxyanhydride to produce the targeted asymmetrical block copolymers. Their molecular structures and physicochemical properties were thoroughly characterized by means of FT-IR, 1H NMR, gel permeation chromatography, differential scanning calorimetry, and wide angle X-ray diffraction. Both the maximal melting temperature and the degree of crystallinity of PCL block within copolymers decreased with increasing the PBLG branches and/or the chain length, demonstrating that the crystallinity of PCL block was progressively suppressed by PBLG block. Meanwhile, the PBLG block within copolymers progressively transformed from β-sheet to α-helical conformation with increasing the PBLG chain length. Consequently, this provides a versatile strategy for the synthesis of biodegradable and biomimetic block copolymers with asymmetrical dendritic topology. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011