| Poly-L-lactide(PLLA)with the merits of good biocompatibility and biodegradability has been applied to bone replacement material.The performance of PLLA rest with its molecular mass and crystal property which is controlled by synthesize techniques and heat treatment,so it is very important to research the synthesize techniques and crystal property of PLLA.In this paper,high purity and high yield L-lactide was prepared by using the new purified method,and poly(L-lactide)was synthesized by ring-opening polymerization with the catalyst Sn(Oct)2.The effects of prepared method of L-lactide,catalyst,time and temperature on reaction were researched.PLLA was been melt at 210℃and then isothermal crystallization was been made in temperature 90-140℃.Crystallization kinetics of PLLA was investigated by Avrami equation and Lauritzen-Hoffmann theory.Different cooling rate was used for investigate the effect of non-isothermal crystallization condition to crystallinity,glass transition temperature and crystal shape of PLLA.Result shows that:the amount of catalyst,reaction time and reaction temperature have influence on the molar mass of PLLA.The best reaction condition is that amounting catalyst 1/12000 and reacting at the temperature of 140 for 24 hours.PLLA exhibits an Avrami crystallization exponent n= 3.0±0.14 In isothermal crystallization in the range from 90℃to 140℃,so crystal of PLLA grows as a bulb form shape.According to Hoffman-Lauritizen theory,two crystallization regime are identified with a transition temperature occurring at around 118℃,crystallization constant is that:Kg(Ⅱ)=6.025×105K2,Kg(Ⅲ)=1.307×106K2,and the value of Kg(Ⅲ)/Kg(Ⅱ) is 2.17.In non-isothermal crystallization heat treatment,the glass transition temperature of PLLA decreases with increase of cooling rate,and the crystallinity at the end of crystallization increases with decreasing cooling rate. Crystallization performed at lower cooling rates(2℃·min-1)is accompanied by a variation of the kinetics around 118℃. |
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