Chain Folding and Unfolding Strucutres of Semicrystalline Polymers Elucidated by Solid-State NMR Spectroscopy

非技术摘要：许多商业塑料是由“半结晶聚合物”制成的，即在工业加工时具有结晶能力的长链分子。由于其优异的机械和热学性能、轻便和易于低成本的制造，它们在我们的日常生活中扮演着重要的角色。因此，各种半晶聚合物被广泛应用于包装、纺织、汽车、飞机零部件、能源、生物兼容材料等领域。为了进一步改善半结晶聚合物的性能，有必要了解它们在固体状态下的详细结构，但尽管在过去的半个世纪里做了许多努力，但对高分子链的三维分子结构仍然没有很好的了解。该项目专注于对以不同方式结晶和加工的样品中半结晶聚合物的分子级结构的基本了解，并可能导致对商业可用聚合物材料性能的改善的预测。PI将使用新的专门光谱技术来探测和了解固态样品中单个聚合物分子的形状。该项目还将包括对研究生和本科生的高级科学培训。他们将经历广泛的聚合物研究，包括聚合物合成、结晶、变形、高级表征和模拟。这些研究成果将发表在科学期刊上，并由研究人员和学生在全国科学会议上发表。技术摘要：聚合物结晶涉及从熔体和溶液状态的随机卷曲到主体和单晶中的折叠链的构象变化，典型的厚度约为5-20 nm。由动力学驱动的聚合物结晶在结晶习性、片层厚度和结晶度等方面产生了独特的特征。已经开发了各种表征工具来揭示层次化的晶体结构。然而，由于实验分辨率的限制，对分子水平构象的理解仍然具有挑战性。PI将使用13C-13C双量子(DQ)核磁共振和选择性同位素13C标记相结合的新方法来阐明半结晶聚合物的折叠链、连续折叠数和相邻的折返分数的重入位置，包括本体和单晶中的聚乙烯、全同立构聚丙烯、全同立构聚1-丁烯和聚乳酸，作为熔体过冷的函数。这项工作旨在结合计算机模拟结果，提供半结晶聚合物在结晶过程和变形过程中的详细分子图像，并将加深我们对聚合物材料结晶过程的理论理解。

NON-TECHNICAL SUMMARY:Many commercial plastics are made of "semicrystalline polymers", i.e. long-chain molecules that have the ability to crystallize when processed industrially. They play important roles in our daily lives due to excellent mechanical and thermal properties, lightness, and easy low-cost fabrication. Thus, various semicrystalline polymers are used in a wide variety of applications including packaging, textiles, automobile, airplane parts, energy, biocompatible materials, and so on. To further improve properties of semicrystalline polymers, understanding of their detailed structure in the solid state is necessary, but, despite many efforts over the last half century, the three-dimensional molecular structures of the polymer chains are still not well understood. This project focuses on fundamental understanding of molecular-level structures of semicrystalline polymers in samples crystallized and processed in various ways, and may lead to predictions of improved properties for commercially available polymeric materials. The PI will be using novel specialized spectroscopic techniques to probe and understand the shapes of individual polymer molecules in the solid-state samples. This project will also include advanced scientific training of graduate and undergraduate students. They will experience a wide range of polymer research covering polymer synthesis, crystallization, deformation, advanced characterizations, and simulations. The research results will be reported in scientific journals and presented by the researcher and students at national scientific meetings.TECHNICAL SUMMARY:Polymer crystallization involves conformational changes from random coils in the melt and solution states, to folded chains in the bulk and in single crystals with a typical thickness of ca. 5-20 nm. The crystallization of polymers driven by kinetics yields unique features in terms of crystal habits, lamellae thickness, and crystallinity, among other features. Various characterization tools have been developed to reveal hierarchical crystalline structures. Nevertheless, the understanding of the molecular-level conformations remains challenging due to limitations of experimental resolutions. The PI will employ a novel approach of 13C-13C double quantum (DQ) NMR combined with selective isotopic 13C labeling to elucidate re-entrance sites of folded chains, successive folding numbers, and adjacent re-entry fractions of semicrystalline polymers, including polyethylene, isotactic polypropylene, isotactic poly(1-butene), and poly(lactic acid) in the bulk and in single crystals as a function of undercooling from the melt. This work is aimed at providing detailed molecular pictures of semicrystalline polymers during crystallization as well as under deformation, in relation also to computer simulation results, and will enhance our theoretical understanding of the crystallization of polymeric materials.