Solid-State NMR Study of the Chain Trajectory and Crystallization Mechanism of Poly(l-lactic acid) in Dilute Solution
Solid-State NMR Study of the Chain Trajectory and Crystallization Mechanism of Poly(l-lactic acid) in Dilute Solution
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DOI：
10.1021/acs.macromol.7b01462
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发表时间：
2017-08
期刊：
影响因子：
5.5
通讯作者：
Shijun Wang;Shichen Yuan;Wei Chen-;Qiming He;You-lee Hong;Toshikazu Miyoshi
中科院分区：
文献类型：
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作者：
Shijun Wang;Shichen Yuan;Wei Chen-;Qiming He;You-lee Hong;Toshikazu Miyoshi
半结晶聚合物的成核和生长机理是高分子科学中一个有争议的话题。在这项工作中，我们调查的链折叠模式，包装结构，和晶体习性的聚（L-乳酸）（PLLA）与相对较低的分子量，Mw = 46 K g/mol，和PDI = 1.4的单晶形成的稀乙酸戊酯（AA）溶液（0.05或0.005重量%）在结晶温度（Tc）为90，50，或100 °C。晶体习性从Tc = 90 °C时的小面菱形急剧变化为Tc = 100 °C时的树枝状，而链在90和0 °C时均采用化学稳定的α堆积结构。比较13 C-标记的PLLA链在与未标记的链以1：9的混合比共混的晶体中的13 C-13 C双量子（DQ）累积曲线的实验和模拟表明，当Tc范围从90 ° C到100 °C时，PLLA链以多行相邻折叠。在不同长度尺度下的结果表明：（i）大部分链在分子内自折叠。
The nucleation and growth mechanisms of semicrystalline polymers are a controversial topic in polymer science. In this work, we investigate the chain-folding pattern, packing structure, and crystal habits of poly(l-lactic acid) (PLLA) with a relatively low molecular weight, ⟨Mw⟩ = 46K g/mol, and PDI = 1.4 in single crystals formed from dilute amyl acetate (AA) solution (0.05 or 0.005 wt %) at a crystallization temperature (Tc) of 90, 50, or ∼0 °C. The crystal habits drastically changed from a facet lozenge shape at Tc = 90 °C to dendrites at ∼0 °C, whereas the chains adopt a thermodynamically stable α packing structure at both 90 and 0 °C. Comparing the experimental and simulated 13C–13C double quantum (DQ) buildup curves of 13C-labeled PLLA chains in crystals blended with nonlabeled chains at a mixing ratio of 1:9 indicates that the PLLA chains fold adjacently in multiple rows when the Tc ranges from 90 to ∼0 °C. The results at different length scales suggest that (i) a majority of the chains self-fold i...