Preparation and Crystallization Kinetics of New Structurally Well-Defined Star-Shaped Biodegradable Poly(L-lactide)s Initiated with Diverse Natural Sugar Alcohols

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• 作者：Qinghui Hao ; Faxue Li ; Qiaobo Li ; Yang Li ; Lin Jia ; Jing Yang ; Qiang Fang ; and Amin Cao
• 刊名：Biomacromolecules
• 出版年：2005
• 出版时间：July 2005
• 年：2005
• 卷：6
• 期：4
• 页码：2236 - 2247
• 全文大小：292K
• 年卷期：v.6,no.4(July 2005)
• ISSN：1526-4602

文摘

This study presents syntheses, structural characterization, and crystallization kinetic investigation of newstructurally well-defined star-shaped poly(L-lactide)s (PLLAs). First, a series of new 3- to 6-arm star-shapedPLLAs were synthesized through SnOct₂ catalyzed ring-opening polymerization of (L)-lactide with naturalsugar alcohols of glycerol, erythritol, xylitol, and sorbitol as the favorable initiators. Subsequently, theirchemical structures were characterized by means of GPC, NMR, and viscometer with respect to the star-shaped structures, demonstrating the well-defined arm structures as evidenced on the g^1/2/g' values, whereg and g' denote the ratios of mean-square radius of gyration and intrinsic viscosity of a star-shaped polymerto those of a linear structural reference with similar absolute molecular weight. Furthermore, spherulitemorphologies and growth rates were studied by a polarized microscopy (POM) for the synthesized star-shaped PLLAs with different molecular weights, and it was found that the more arms of a star-shapedPLLA finally resulted in a lower spherulite growth rate. With regard to the crystallization kinetics of thesestar-shaped PLLAs, isothermal and nonisothermal crystallization were examined by differential scanningcalorimeter (DSC). It was found that Avrami exponent n values of isothermal crystallization were almostindependent of the isothermal crystallization temperature T_c for different series of star-shaped PLLAs. Incontrast, the values of Avrami exponent n were observed to strongly depend on the star-shaped structureswith different arms, implying their distinct nucleation mechanisms, and the more arms of a star-shapedPLLA led to a slower isothermal crystallization rate. On the basis of a modified Avrami equation, new lightwas shed on the nonisothermal crystallization kinetics for the star-shaped PLLAs, and the activation energieswere found to vary from 146.86 kJ/mol for the linear PLLA EG-3 to 221.23 kJ/mol of the star-shaped S-3,demonstrating much decreased crystallizabilities of star-shaped PLLAs with more arms.