Synthesis, Crystallization Kinetics, and Spherulitic Growth of Linear and Star-Shaped Poly(L-lactide)s with Different Numbers of Arms

Well-defined linear poly(L-lactide)s with one or two arms (LPLLA and 2LPLLA, respectively)and star-shaped poly(L-lactide)s with four or six arms (4sPLLA and 6sPLLA, respectively)were synthesized and then used for the investigation of the thermal properties, isothermal crystallization kinetics, and spherulitic growth. The maximal melting temperature, the cold-crystallization temperature, and the degree of crystallinity of these poly(L-lactide)polymers decreased with an increasing number of arms in the macromolecule. Moreover, the isothermal crystallization rate constant (K)of these poly(L-lactide)polymers decreased in the order of KLPLLA > K2LPLLA > K4sPLLA > K6sPLLA2, which was consistent with the variation trend of the spherulitic growth rate (G). Meanwhile, both K and G of 6sPLLA slightly increased with the increasing molecular weight of the polymer. Furthermore, both LPLLA and 2LPLLA presented spherulites with good morphology and apparent Maltese cross patterns, whereas both unclear Maltese cross patterns and imperfect crystallization were observed for the star-shaped 4sPLLA and 6sPLLA polymers. These results indicated that both the macromolecular architecture and the molecular weight of the polymer controlled K, G, and the spherulitic morphology of hese poly(L-lactide)polymers.