流场中聚乳酸/聚碳酸酯共混体系的酯交换反应及其形态结构研究

TRANSESTERIFICATION BETWEEN POLY(LACTIC ACID) AND POLYCARBONATE UNDER FLOW FIELD AND ITS INFLUENCE ON MORPHOLOGY OF THE BLENDS

选用钛酸四丁酯作为聚乳酸(PLA)/聚碳酸酯(PC)的酯交换反应催化剂,通过透射电子显微镜(TEM)和核磁共振氢谱(1H-NMR)研究了流场中不同组分比的PLA/PC共混体系酯交换反应机理及酯交换反应对不同组分比的共混体系相形态的影响.研究发现,无论在PLA/PC共混体系中是否含有催化剂,酯交换反应次数、参与酯交换反应的PC的含量、生成的共聚物中PC链段的含量及生成的共聚物的总质量和总摩尔数均随组分中PLA含量的增加而增加,催化剂的加入更拉大了这种差距.主要原因是与PC作为连续相相比,当PLA作为连续相时PLA链段沿界面的取向程度更高,从而导致进行多次酯交换反应的几率增加.添加催化剂后,影响酯交换反应的主导因素发生变化,从而导致PLA/PC 30/70体系界面反应的机理发生改变.钛酸四丁酯有效地促进了PLA/PC体系的酯交换反应,使分散相的尺寸都得到不同程度降低,尤其当PLA为连续相时催化产生的共聚物的总摩尔数更多,从而使PLA为连续相时的分散相粒径较PC为连续相时降低的更多.

Tetrabutyl titanate has been selected as transesterification catalyst of poly（lactic acid） （PLA） and polycarbonate （PC） to investigate transesterification mechanism between poly（lactic acid） （PLA） and polycarbonate （PC） and the influence of transesterification reaction on the morphology of blends with different compositions.It is found that the transesterification reaction time,the fraction of reacted PC,the composition of polycarbonate in copolymer,the weight and mole number of PC-co-PLA copolymer increase substantially with the increasing of the composition of poly（lactic acid） in the blends no matter the catalyst is added or not.The difference in the amount of the reacted PC between 70/30 and 30/70 blends increases further with the addition of catalyst due to the easier alignment of PLA segments in copolymers along the interface when poly（lactic acid） is the continuous phase as compared with polycarbonate to be the continuous phase.Moreover,the interfacial reaction mechanism in PLA/PC 30/70 blend is found to be changed with the addition of catalyst since the dominated factor that influences the ester exchange reaction has changed.Furthermore,the domain size of dispersed phase decreases due to the promotion of transesterification by tetrabutyl titanate.Especially,larger mole number of copolymer in blends with PLA as continuous phase is produced when catalyst is added,which causes a more evident decrease in domain size in blends with PLA as continuous phase as compared to that in blends with PC as continuous phase.