Versatile Synthesis of Asymmetrical Dendron-Like/Dendron-Like Poly(ε-Caprolactone)-b-Poly(γ-Benzyl-L-Glutamate) Block Copolymers

Dendron-like/dendron-like poly(epsilon-caprolactone)-b-poly(gamma-benzyl-L-glutamate) block copolymers with asymmetrical topology (PCL208-b-PBLG(n), 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 PCL208 precursor with eight branches was synthesized from the controlled ROP of epsilon-caprolactone, and then click conjugated with azido focal point poly(amido amine) dendrons to generate the PCL208-dendrons with multiple primary amine groups. The PCL208-dendrons were further used as macroinitiators for the ROP of gamma-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, H-1 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 beta-sheet to alpha-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. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3491-3498, 2011