环氧丙烷聚醚三元醇/左旋聚乳酸三枝链嵌段共聚物的结晶行为

Crystallization Behavior of Triarm Poly(propylene oxide block L-lactide) Copolymer

采用DSC对环氧丙烷聚醚三元醇/左旋聚乳酸三枝链嵌段共聚物(PPO-b-PLLA)的熔体结晶行为进行了研究.在388～407K范围内,分别采用Avrami方程和Arrhenius方程进行了结晶动力学计算.Avrami指数n值约为2.2,表明共聚物以二维生长方式进行晶体生长.基于LH结晶理论,对三枝链嵌段共聚物的结晶机理进行了探讨.实验发现该体系共聚物的RegimeⅡ和RegimeⅢ转变温度随着n(PO)∶n(LA)的增大而变化,Kg(Ⅲ)/Kg(Ⅱ)=2.0～2.2,与LH理论预期值吻合.实验结果表明三枝链的PPO链段对PLLA链段的结晶有很大影响,使其成核较均聚物困难.链折叠自由能σe和链折叠功q均高于PLLA的值.

Melt-crystallization behavior of triarm poly（propylene oxide block L-lactide） （PPO-b-PLLA） copolymer was investigated by means of DSC. Kinetics of melt-crystallization of the samples were investigated in temperature range from 388 to 407 K, and the results were treated with Avirami equation and Arrhenius equation. Based on LauritzenHofmann nucleation and growth theory, the crystallization mecha-nisms of triarm PPO-b-PLLA copolymer was analyzed, presenting the transition from regime II to regime III with the variation of the chemical structure. And value of Kg（Ⅲ ）/Kg（Ⅱ ） was in the range of 2.0～2.2, which agrees with the value by LH theory. Both values of fold surface free energy （σe） and chain folding work （q） of the copolymer were much higher than those of PLLA homopolymer, due to the crystallization process of PLLA segments in copolymer hided by bonding PPO segments. And the lower surface nucleation rate occurred in the case of the triarm PPO-b-PLLA copolymer.