Zhou Wenxuan, Wang Kun, Wang Shijun, Yuan Shichen, Chen Wei, Konishi Takashi, Miyoshi Toshikazu
Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909, United States.
State Key Lab of Pollution Control and Resource Reuse Study College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
ACS Macro Lett. 2018 Jun 19;7(6):667-671. doi: 10.1021/acsmacrolett.8b00297. Epub 2018 May 23.
Poly(l-lactic acid) (L)/poly(d-lactic acid) (D) blends form a stereocomplex (SC) at a mixing ratio of 7/3-3/7. The stoichiometry and packing structure of L/D in the SC are controversial topics because the SC is semicrystalline and because the enantiomeric pair has the same chemical structure. In this study, both the stoichiometry and packing structure of 33% C CH-labeled () L/nonlabeled D blends at mixing ratios of 7/3-3/7 were investigated by using solid-state (SS) NMR. The C CO signals in natural abundance provided the fractions of the SC (Φ), α, and amorphous regions of -L/D blends. Moreover, the 33% CH-labeled signals could determine the fraction of only -L in the SC (Φ) and amorphous region. These two data sets allowed us to determine the stoichiometry of -L/D in the SC (Φ/Φ) to be 1/1. C-C double-quantum (DQ) buildup curves of -L in the SC followed one universal curve even at different mixing ratios. Comparison of the experimental and simulated DQ curves led to the conclusion that all SC crystals adopt a regular packing structure at varied mixing ratios.
聚（L-乳酸）（L）/聚（D-乳酸）（D）共混物在7/3至3/7的混合比例下形成立体复合物（SC）。由于SC是半结晶的，且对映体对具有相同的化学结构，因此SC中L/D的化学计量和堆积结构是有争议的话题。在本研究中，通过使用固态（SS）NMR研究了混合比例为7/3至3/7的33% C CH标记的（）L/未标记D共混物的化学计量和堆积结构。天然丰度下的C CO信号提供了-L/D共混物的SC（Φ）、α和无定形区域的分数。此外，33% CH标记的信号可以确定SC（Φ）和无定形区域中仅-L的分数。这两组数据使我们能够确定SC中-L/D的化学计量（Φ/Φ）为1/1。即使在不同的混合比例下，SC中-L的C-C双量子（DQ）积累曲线也遵循一条通用曲线。实验和模拟DQ曲线的比较得出结论，在不同的混合比例下，所有SC晶体都采用规则的堆积结构。
