Critical size and formation mechanism of secondary nuclei in melt- crystallized polylactide stereocomplex crystals
Critical size and formation mechanism of secondary nuclei in melt- crystallized polylactide stereocomplex crystals
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熔融结晶聚丙交酯立体络合物晶体中二次核的临界尺寸和形成机制
DOI：
10.1021/acs.macromol.2c02494
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发表时间：
--
期刊：
影响因子：
5.5
通讯作者：
Jun Xu
中科院分区：
文献类型：
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作者：
Zhiqi Wang;Ranlong Duan;Xuan Pang;Rongling Wu;Baohua Guo;Jun Xu
揭示限速有序化过程的分子机理和确定限速有序化过程的长度尺度一直是聚合物结晶领域的一个挑战。在此之前，我们提出了一种根据不同稀释率下成核动力学的变化来确定单组分晶体中临界晶核尺寸的理论。在这里，我们进一步将这个理论推广到由聚(L-丙交酯)和聚(D-丙交酯)组成的聚乳酸立体络合物晶体(SCS)。通过随机共聚合稀释丙交酯单元或丙交酯和丙交酯单元，得到了临界二次核中丙交酯单元的数目和两种单元的数目。结果表明，在140~170℃熔融结晶时，Sc大块晶体的临界二次晶核由22-27l-丙交酯单元和相同数量的d-丙交酯单元组成，这些重复单元形成两个聚L-丙交酯茎和两个聚d-丙交酯茎。SC次生核中的四个茎选自大约三到四个链。根据链的数目，至多有三分之一的聚乳酸链在熔融结晶的SC的二次晶核中有一次相邻的再入折叠。这些结果为Sc晶体熔融结晶过程中的有序化过程提供了丰富的信息，有助于理解Sc晶体的结晶机理。
Revealing the molecular mechanism and determining the length scale of the rate-limiting ordering process have been a challenge in the field of polymer crystallization. Previously, we proposed a theory to determine the size of critical nuclei in single-component crystals from the variation of nucleation kinetics with different dilution ratios. Here, we further extend this theory to polylactide (PLA) stereocomplex crystals (SCs) consisting of poly(l-lactide) and poly(d-lactide). By diluting onlyl-lactide units or bothl-lactide andd-lactide units via random copolymerization, the number ofl-lactide units and that of two types of units in a critical secondary nucleus were obtained. The results show that a critical secondary nucleus of an SC bulk crystal consists of 22–27l-lactide units and the same number ofd-lactide units when crystallized from melt at temperatures ranging from 140 to 170 °C. These repeating units form two poly(l-lactide) stems and two poly(d-lactide) stems. The four stems in a secondary nucleus of SC are chosen from approximately three to four chains. According to the number of chains, at most one-third of PLA chains has once adjacent re-entry folding in the secondary nuclei of SC crystallized from melt. These results provide rich information on the ordering process during the melt crystallization of SC crystals and are beneficial for understanding the crystallization mechanism.