摘要
聚乳酸(PLA)是具有可生物降解性和生物相容性的高分子材料,是医学领域中最具吸引力的材料之一,同时也是一种具有广泛应用前景的环保型高分子新材料。尤其是星形聚乳酸、星形嵌段聚乳酸、梳形聚乳酸等具有奇特微观结构的聚合物往往都能表现出特别的宏观性质。因此有必要研究和开发工序简单、溶解性能好、成本低廉而更有实用价值的星形支化聚乳酸。
首先以乳酸为原料,以季戊四醇为支化剂,采用SnCl_2·2H_2O/TSA复合催化剂合成了星形支化聚L-乳酸。结果表明,较适宜的熔融缩聚工艺条件为:催化剂SnCl_2·2H_2O加入量为0.5wt%,L-乳酸与支化剂季戊四醇(PET)的摩尔比为1500,聚合温度为180℃,在1.5kPa聚合12小时,得到分子量为53000左右的星形聚L-乳酸。
研究了不同结构的聚乳酸的体外水解行为,结果表明星形聚L-乳酸具有比较好的降解性能。
用差示扫描量热法(DSC)研究了星形聚L-乳酸的结晶和熔融行为。DSC研究结果发现,熔融缩聚制备出的星形聚L-乳酸热结晶时基本观察不到结晶峰。经过等温热结晶处理后的星形聚L-乳酸再次升温扫描时候出现了双熔融峰的现象,其中低熔融峰的峰值温度(T_m(L))与等温结晶温度的对数值成线性增长关系,而高熔融峰的峰值温度(T_m(H))与等温结晶温度基本无关。
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 SnCl_2·2H_2O/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% SnCl_2·2H_2O 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.
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