Hong You-Lee, Miyoshi Toshikazu
Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909, United States.
ACS Macro Lett. 2014 Jun 17;3(6):556-559. doi: 10.1021/mz500196s. Epub 2014 May 29.
Despite tremendous efforts over the last half-century to elucidate the chain-folding (CF) structure of semicrystalline polymers, the re-entrance sites of folded chains, the successive CF number , and the adjacent re-entry fraction have not been well characterized due to experimental limitations. In this report, C-C double-quantum (DQ) NMR was used to determine for the first time the detailed CF structure of C CH-labeled poly(1-butene) (PB1) in solution-grown crystals blended with nonlabeled PB1 across a wide range of crystallization temperatures (s). Comparison of the results of DQ experiments and spin dynamics simulations demonstrated that the majority of individual chains possess completely adjacent re-entry structures at both = 60 and ∼0 °C, as well as indicated that a low polymer concentration, not kinetics, leads to cluster formations of single molecules in dilute solution. The changes in crystal habits from hexagonal shapes at = 60 °C to rounded shapes at ∼0 °C (kinetic roughness) are reasonably explained in terms of kinetically driven depositions of single molecule clusters on the growth front.
尽管在过去半个世纪里人们付出了巨大努力来阐明半结晶聚合物的链折叠（CF）结构，但由于实验限制，折叠链的再入位点、连续CF数以及相邻再入分数尚未得到很好的表征。在本报告中，首次使用碳 - 碳双量子（DQ）核磁共振来确定在广泛的结晶温度（s）范围内与未标记的聚1 - 丁烯（PB1）共混的溶液生长晶体中，碳 - 碳标记的聚1 - 丁烯（PB1）的详细CF结构。DQ实验结果与自旋动力学模拟结果的比较表明，在60℃和约0℃时，大多数单链都具有完全相邻的再入结构，同时还表明，在稀溶液中，低聚合物浓度而非动力学导致单分子形成聚集体。从60℃时的六边形晶体习性到约0℃时的圆形晶体习性（动力学粗糙度）的变化，可以通过单分子聚集体在生长前沿的动力学驱动沉积得到合理的解释。
