Two stereocomplexes (SCs) with different molecular weights in poly(L-lactide) (PLLA-49k and PLLA-163k) were prepared by mixing equal amounts of poly(D-lactide) (PDLA) and PLLA via the solution method. The exclusive formation of SCs was achieved in SC-PLLA-49k, whereas both homocrystallites (HCs) and SCs were observed in SC-PLLA-163k. Two blends were subjected to further processing via the ultrasonic microinjection molding technique at varying mold temperatures, yielding amorphous samples. As the samples were heated, the heating induced structural reorganization occurs with the concurrent SCs and HCs for all samples at ca. 80 °C. The degree of crystallinity for HCs XHC exhibits a positive correlation with the mold temperature, whereas the degree of crystallinity for SCs XSC shows a negative dependence on mold temperature for both systems. This behavior can be tentatively explained as follows. Firstly, the demixing of enantiomeric PLA chains occurs in the melt state as evidenced by twice heating measurements of blends. The degree of chain segregation is expected to increase with the increase in mold temperature due to lower supercooling, resulting in a decrease of PLLA/PDLA clusters (SC nuclei). Secondly, a high mold temperature is beneficial for the formation of HC nuclei as the chain mobility is improved. The reformulation of SC nuclei is difficult because of a longer diffusion distance required for PLA molecules. The coexistence of SC and HC nuclei causes the simultaneous appearance of SCs and HCs during heating of samples. As HCs start to melt, a transition from HCs to SCs occurs accompanied by a continuous increase in XSC. For both systems, a maximum of XSC is reached when SCs begin to melt followed by a mold temperature independent evolution of XSC upon further heating. Such a maximum is larger in the low molar mass system because it is less entangled. The reservation of SC nuclei is demonstrated by a comparison of the structural evolution and isothermal cold crystallization behavior between the two blends and their ultrasonic microinjection molded samples.

中文翻译：

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超声微注射成型聚丙交酯立体复合物在加热过程中的结构演变


通过溶液法混合等量的聚(D-丙交酯)(PDLA)和PLLA，制备了两种不同分子量的聚(L-丙交酯)立体络合物(SC)(PLLA-49k和PLLA-163k)。 SC-PLLA-49k 中实现了 SC 的排他形成，而 SC-PLLA-163k 中同时观察到同晶 (HC) 和 SC。通过超声波微注射成型技术在不同的模具温度下对两种共混物进行进一步加工，产生非晶态样品。当样品被加热时，加热诱导的结构重组发生在所有样品的同时 SC 和 HC 的情况下。 80℃。对于两个系统，HC XHC 的结晶度与模具温度呈正相关，而 SC XSC 的结晶度与模具温度呈负相关。这种行为可以暂时解释如下。首先，对映体 PLA 链的分层发生在熔融状态，共混物的两次加热测量证明了这一点。由于过冷度较低，预计链偏析程度会随着模具温度的升高而增加，从而导致 PLLA/PDLA 簇（SC 核）减少。其次，高模具温度有利于HC核的形成，因为链迁移率得到改善。 SC 核的重构很困难，因为 PLA 分子需要更长的扩散距离。 SC 和 HC 核的共存导致样品加热过程中 SC 和 HC 同时出现。当 HC 开始熔化时，从 HC 到 SC 的转变发生，同时 XSC 不断增加。 对于这两种系统，当 SC 开始熔化时，XSC 达到最大值，随后进一步加热时 XSC 会与模具温度无关地演化。这样的最大值在低摩尔质量体系中更大，因为它较少纠缠。通过比较两种共混物及其超声微注射成型样品之间的结构演变和等温冷结晶行为，证明了 SC 核的保留。