Synthesis, characterization and nanoparticle formation of star-shaped poly(L-lactide) with six arms

Well-defined star-shaped poly( L-lactide) with six arms ( sPLLA) was synthesized via the ring-opening polymerization of L-lactide using dipentaerythritol as initiator and stannous octoate as catalyst in bulk at 125 C. The effects of molar ratios of both monomer to initiator and monomer to catalyst on the molecular weights of as-synthesized sPLLA polymers were in detail investigated. The molecular weights of sPLLA polymers linearly increased with the molar ratio of monomer to initiator, and the molecular weight distribution was narrow ( M-w/M-n = 1.04- 1.12). However, the molar ratio of monomer to catalyst had no apparent influence on the polymer molecular weight. Moreover, the maximal melting point, the crystallization temperature, and the degree of crystallinity of sPLLA polymers increased with the increasing molecular weight, meanwhile they exhibited a spherulitic morphology. Furthermore, spherical nanoparticles ( less than 100 nm) could be generated by direct injection of sPLLA solutions into distilled water, and the average size of nanoparticles could be adjusted through both the macromolecular architecture and the polymer molecular weight, respectively.