Hybrid polypeptide/polylactide copolymers with short phenylalanine blocks

Abstract

Hybrid copolymers constituted by short l-phenylalanine (Phe) blocks (i.e., Phen with n ranging from 2 to 25) and l-lactide blocks of different length are synthesized and characterized. The diblock structure is obtained by ring opening polymerization of lactide using a Phe-oligopeptide as macroinitiator. The length of the poly(l-lactide) (PLLA) block is controlled through the [lactide]/[macroinitiator] ratio. Morphologic studies of such hybrid copolymers indicate that the assembly of PLLA can be controlled by introducing short Phe blocks. Spherulites with both positive and negative birefringence are achieved in melt crystallization as a consequence of different lamellar distributions. Instead, a high variety of structures are detected in solution-crystallized samples. Specifically, lozenge single crystals, flower-like crystals, fibrillar structures, compact spheres, ringed sperulites, dendritic structures, microfibers, and braid-like microstructures are observed. Some of the detected morphologies are characteristic of self-assembled Phe-oligopeptides, suggesting that Phe-blocks play a crucial role in the self-assembly properties.