Synthesis And Studies Of Star-shaped PLLA

Polylactide(PLA) is a biodegradable and biocompatible crystalline polymer which has resultant environmental advantages among all synthetic polymers. Especially, the well-defined macromolecular architecture such as star-shaped PLA, star block PLA and comb-like PLA attracted considerable interest due to their various functions and properties resulting from their special structures. Therefore, it is reasonable to make further efforts to investigate special structure polylactide, such as star-shaped PLA which with lower holding water property and cost-efficient processing.In this study, the star-shaped poly (L-lactide) (SPLLA) was synthesised and its properties were studied, the melt polycondensation of 4-arms star-shaped PLLA synthesized by the well-known SnCl₂·2H₂O/TSA and pentaerythritol (PET) have been investigated in detail. Degradation, crystallization and melting behaviors of resulting star-shaped PLLA had been investigated. Star-shaped with weight-average molecular weight of about 53000 was successfully synthesized with 0.5wt% SnCl₂·2H₂O at 180℃and under 1.5kPa for 12 hours.The hydrolytic degradation of different kinds of PLLA was studied. With almost the same molecular weights, star-shaped PLLA possessed the best degradability.Differential scanning calorimetry (DSC) and polarizing microscope were utilized to characterize the crystallization and melting behaviors of star-shaped PLLA.In the DSC study, it is found that in the hot isothermal crystallization process, the crystallization peaks were very weak. When the sample gone through hot crystallization were reheated, no crystallization peak but double melting peak, a low-temperature melting peak(L peak)and a high-temperature melting peak(H peak), were observed. The L peak temperature(T_m(L)) increased linearly with logarithm of the isothermal crystallization temperature while the H peak temperature (T_m(H)) kept constant.