立构二嵌段聚乳酸微纳米纤维的制备与结晶性能

Preparation and Crystallization Properties of di-Stereoblock Polylactides Micro/Nanofibers

以羟基封端D型聚乳酸(HO-PDLA)作为大分子引发剂引发L-丙交酯(L-LA)本体开环聚合制备了不同数均分子量的线性立构二嵌段聚乳酸(di-sb-PLA),并应用静电纺丝技术制备了亚微米级纤维。结果表明:所合成的di-sb-PLA形成了完全的立构复合(sc)晶型,熔点均超过了215℃,热稳定性得到改善并表现出良好的韧性,浇注膜的断裂伸长率可达250%。电纺纤维膜中聚乳酸(PLA)分子链呈高度无定形状态,通过冷结晶生成大量的sc晶体,比熔融淬火样有更强的结晶能力。sc晶体的生成与甲基和羰基的相互作用有关。

By controlling the molar ratio of D-enantiomer to L-enantiomer of the lactide,a series of di-stereoblock polylactides(di-sb-PLA)bearing similar block sequences between poly(D-lactide)(PDLA)and poly(L-lactide)(PLLA)were synthesized by ring-opening polymerization of L-lactide(L-LA)using hydroxyl terminated PDLA(HO-PDLA)as a macromolecular initiator.Micro/nanofibers were then fabricated by electrospinning di-sb-PLAs from their dichloromethane(DCM)and hexafluoroisopropanol(HFIP)mixtures.The thermal and mechanical properties,fiber morphology and crystallization properties of di-sb-PLAs were analyzed.The results of DSC showed that di-sb-PLA formed complete stereocomplex(sc)crystals with the melting point higher than 215℃,and no homocrystal was formed.The crystallization ability of sc was decreased with an increase in length of each block.It is worth to note that sc of stereoblock PLA was formed on molecular-scale without post-processing compared with PLA homopolymers,which enhanced the heat resistance and improved the elongation at break of solution-cast film to 250%without losing tensile strength,especially for di-sb-PLAs that has higher molecular weight.After electrospinning,the as-spun micro/nanofibers of di-sb-PLA were homogeneous and smooth,in which PLA molecules were almost amorphous.A large amount of sc crystals were then formed by cold crystallization during heating-up process,and the melting points of sc crystals in these fibers were increased by 8℃ as compared with the melt-quenched samples.Moreover,the results of in-situ ATR-FT-IR at variable temperature disclosed that the formation of sc crystals was related to the interactions between side methyl groups and carbonyl groups in PLA.The results hold promise for the further application of di-sb-PLA.