The Synthesis And Crystal Properties Of Star-Shaped Poly(L-Lactide)

In this study, the ring opening polymerization of L-lactide was catalyzed by the Sn(Oct)2with the aid of different nature sugar alcohols as the initiators. Through controlling the molar ratios of monomer to sugar alcohol, we obtained the certain molecular weight multi-arm star-shaped PLLAs which were measured by gel permeation chromatography (GPC). To confirm the multi-arm structures of star-shaped PLLA, the1H NMR spectra of sugar alcohol after initiating the polymerization of L-lactide was analyzed. These results clearly confirmed that each hydroxyl group of sugar alcohols initiate the polymerization of L-lactide, resulting in the formation of multi-arm star-shaped PLLAs. Liner PLLA (L-PLLA)(Mn=4.5x104g·mol-1, Mw=1.1x105g·mol-1) used in the study was supplied from Mitsubishi Plastic Inc.The size of5-arm PLLA spherulites was smaller than that of the linear counterpart at the same crystallization temperature (Tc). This can be explained that the existence of xylitol, which acted as the initiator of5-arm PLLA, accelerated the nucleation and increased the number of crystal nucleus.The crack behavior was observed in melt-crystallization5-arm PLLA during the cooling process, instead of the linear counterpart. The reasons for crack patterns were proved to be relevant to molecular weight, crystallization temperature and thermal shrinkage.It was found that star-shaped PLLA with different number of arms during the same non-isothermal crystallization process, along with the increase of the number of arm, the starting of crystallization temperature and peak of crystallization temperature became lower. This suggested that along with the increase of the arm number, crystallization became more difficult.At different crystallization temperature, the star-shaped PLLA as well as linear PLLA, their crystal form may take a change. At the low temperature crystallization, PLLAs tend to generate a' crystal, while at high crystallization temperature they tend to generate more stable a crystal. With the increase of the arm of star-shaped PLLA, the temperature of crystal change declined slightly.Among the synthetic star-shaped PLLA in the study, their thermal stability increased with the increasing number of arm. It also indicated that the topological structure of PLLA would have an influence on its thermal stability.