Study On The Structure And Properties Of Poly (Lactide) Blend System

Polylactic acid(PLA)is widely used due to its good biocompatibility,biodegradability,and excellent mechanical properties.However,due to its slow crystallization rate,poor heat resistance and other factors limit its further application.The combination of L-polylactic acid(PLLA)and D-polylactic acid(PDLA)can form stereocomplex,the melting point of which is about 50? higher than that of homopolymer crystals.At the same time,it is an effective nucleating agent for PLA and has great prospects in modifying PLA.In this paper,a series of polystyrene-block-d-polylactic acid(PS-b-PDLA)block copolymers with different molecular weights were prepared and blended with L-polylactic acid to explore crystallization properties of the block copolymers,and the relationship between crystallization properties with the structure of the blended system.The main research contents are as follows:A series of block copolymers with controllable molecular weight PS-b-PDLA were prepared using hydroxyl-terminated small molecule chain transfer agents as initiators,combined with living radical polymerization and ring-opening polymerization.The effect of polystyrene(PS)blocks on the crystallization properties of PDLA blocks was studied.The results showed that PS blocks hindered the crystallization of PDLA blocks.A series of PS-b-PDLA/PLLA blends with different PDLA contents were prepared and the effect of PS blocks on the crystallization behavior of the blend system was studied.The study shows that the introduction of high molecular weight PS blocks makes the crystallization of the blend system more difficult The low molecular weight PS block accelerates the crystallization of the blend by promoting the formation of stereocomplex.By preparing a series of PS-b-PDLA/PLLA blends with equal amounts of PLLA and PDLA and exploring the effect of PS blocks on the stereocrystalline crystallization of the blend system,the results show that the high molecular weight PS blocks pass a significant phase separation the behavior restricts the mobility of the PLA molecular chain and weakens the contact ability between PDLA and PLLA.It inhibits the formation of stereocomplex.The low molecular weight PS block improves the miscibility level of PDLA and PLLA by forming a microphase separation structure with PLA,the ability of the block to hinder the movement of the PLA molecular chain is weak,so that the content of the formed stereocomplex is increased.