Study On The Crystallization And Degradation Behavior Of Aliphatic Polymers With Various Structures

Both crystalline aliphatic poly (L-lactic acid) (PLLA) and poly (?-caprolactone) (PCL) are promising as scaffolds in tissue engineering because of the excellent biocompatibility and biodegradability. However, PLLA is hard but brittle while PCL possesses high tenacity but low degradation rate. As a consequence, it is feasible to improve the performance of the polymers and adjust the surfaces structure, morphology and degradation rate by combining these two polymers with physical or chemical means, which can extend the application in biology and medical fields. In this work, a series of binary polymer systems were constructed with PLLA and PCL as structural unit, and the effects of chemical structure and composition on the compatibility, crystallization and degradation behavior of the polymer systems were systematically studied. The results will provide theoretic foundation for regulating the surface structure, morphology and degradation rate. The main work is as follows:Firstly, a series of PLLA, PCL, PLLA-b-PCL and PLLA-co-PCL with well-defined structure and tunable composition are synthesized with monohydric or dihydric alcohols as initiators. Consequently, the binary polymers with various chemical structures are obtained, namely PLLA/PCL blends, PLLA-b-PCL block copolymers and PLLA-co-PCL random copolymers.Then, the effect of chemical structure and composition on compatibility, crystallization and degradation behavior is studied by the measurement of glass transition temperature, one-step and two-steps isothermal crystallization, non-isothermal crystallization and selective degradation. It is indicated that the compatibility between PLLA and PCL phase can be modified by adjusting the chemical structure and it can achieve thermodynamic degree of compatibility for random copolymers. Crystalline/crystalline binary polymers show complicated crystallization behaviors which is influenced not only by chemical structure but also by binary composition and heat treatment condition. Meanwhile, the results indicate that the degradation rate and surface morphology can be modified by adjusting chemical structure, composition and condensed state structure, which supply a simple and effective method for extending the application in tissue engineering field.