Unique crystallization behavior of poly(L-lactide)/poly(D-lactide) stereocomplex depending on initial melt states
Unique crystallization behavior of poly(L-lactide)/poly(D-lactide) stereocomplex depending on initial melt states
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DOI：
10.1016/j.polymer.2008.10.028
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发表时间：
2008-12-08
期刊：
影响因子：
4.6
通讯作者：
Li, Suming
中科院分区：
文献类型：
--
作者：
He, Yong;Xu, Ying;Li, Suming
当聚L-乳酸（PLLA）/聚D-乳酸（PDLA）共混物（50/50）在特定的熔融条件下，观察到PLLA/PDLA立体复合物独特的结晶行为。以乳酸锌为催化剂，通过L-或D-丙交酯开环聚合，合成了聚乳酸（PLLA）和聚乳酸（PDLA）。通过溶液混合、真空干燥制备了PLLA/PDLA共混物。采用DSC、XRD、NMR和ESEM等分析手段对共混物进行熔融结晶。立体复合物仅由相对低分子量的PLLA和PDLA的50/50共混物形成。令人惊讶的是，立体复合物的结晶明显抑制时，较高的熔融温度和较长的熔融时间，在均聚物的结晶。考虑到PLLA和PDLA链之间的主要相互作用，提出了一种新的熔融过程模型来说明这种行为。据推测，PLLA和PDLA链对将保持它们的相互作用（熔融记忆）时，立体复合物晶体顺利熔化，从而导致在一个不均匀的熔体，可以很容易地结晶。在较高的温度或较长的熔化时间下，熔体逐渐变得均匀。PLLA和PDLA链段之间的强相互作用随机分布在均匀的熔体中，从而防止随后的立体复合物结晶。然而，均匀熔体可以通过溶解在溶剂中恢复其结晶能力。(c)2008爱思唯尔有限公司保留所有权利。
A unique crystallization behavior of poly(L-lactide) (PLLA)/poly(D-lactide) (PDLA) stereocomplex was observed when a PLLA/PDLA blend (50/50) was subjected to specific melting conditions. PLLA and PDLA were synthesized by ring opening polymerization Of L- or D-lactide using zinc lactate as catalyst. PLLA/PDLA blend was prepared through solution mixing followed by vacuum drying. The blend was melted under various melting conditions and subsequent crystallization behaviors were analyzed by using DSC, XRD, NMR and ESEM. Stereocomplex was exclusively formed from the 50/50 blend of PLLA and PDLA with relatively low molecular weights. Surprisingly, stereocomplex crystallization was distinctly depressed when higher melting temperature and longer melting period were applied, in contrast to homopolymer crystallization. Considering predominant interactions between PLLA and PDLA chains, a novel model of melting process is proposed to illustrate this behavior. It is assumed that PLLA and PDLA chain couples would preserve their interactions (melt memory) when the stereocomplex crystal melts smoothly, thus resulting in a heterogeneous melt which can easily crystallize. The melt could gradually become homogeneous at higher temperature or longer melting time. The strong interactions between PLLA and PDLA chain segments are randomly distributed in a homogeneous melt, thus preventing subsequent stereocomplex crystallization. However, the homogeneous melt can recover its ability to crystallize via dissolution in a solvent. (c) 2008 Elsevier Ltd. All rights reserved.