Synthesis and characterization of star-shaped poly (L-lactide)s initiated with hydroxyl-terminated poly(amidoamine) (PAMAM-OH) dendrimers

Novel biodegradable star-shaped polymers that consist of poly(L-lactide) (PLLA) arms and a starburst PAMAM dendrimer core were prepared by ring-opening polymerization of L-lactide with PAMAM-OH dendrimer (generation 1-4) initiators and a stannous octoate catalyst in bulk at 130 degreesC. The molecular weights of the star-shaped polymers were measured by GPC, H-1 NMR, and SLS. It was found that the molecular weight of the synthesized star-shaped polylactides can be controlled by variation of the generation of the dendrimer initiators and the molar ratio of monomer to initiator. Effects of molecular weight and number of arms on the thermal properties and hydrolytic degradation of the star-shaped polylactides were investigated. For polylactides initiated with the same dendrimer initiator, the melting temperature and crystallinity increased with increasing molecular weight. For star-shaped polylactides initiated with dendrimer initiators with different generations, the melting point, crystallinity, crystallization rate, and maximum decomposition temperature decreased as the number of arms increased, while the corresponding hydrolysis rate increased.