Kinetic Control of Crystalline Order in Olefin-Based Polymers

建议开展技术总结研究，以提高对无取向块体结晶聚烯烃的链结构、相结构、结晶动力学和形态之间相互作用的认识。其目的是使用特征良好的系统来理解这种相互作用，这些系统充当预测更复杂的商业系统行为的模型。然后，分子可以被定制成具有独特的晶体形态和性质。我们试图从第一性原理来理解结晶动力学在最终结晶状态发展中的作用。令人感兴趣的是过冷对核大小的影响，启用时折叠的性质，以及对序列特定大分子堆积的影响。使用在卤素取代中具有精细控制的聚乙烯分子作为模型系统来预测动力学控制的多态转变，寻求对初级链沉积和后续排列的进一步见解，因为它们与聚合物结晶路径的经典和新观点有关。在茂金属制造的聚丙烯和高α-烯烃无规共聚物的共混物中，序列长度分布在多晶性行为和演变的结晶相结构中的作用将针对广泛的组成进行讨论。非技术总结建议的主要工作涉及两种主要的商业聚烯烃，聚乙烯和聚丙烯。由于它们占所有合成聚合物年产量的一半以上，因此产品的任何改进，无论是通过支化体系结构、加工速度或明智的组分混合，都将在美国和世界经济中产生重大影响。这些聚烯烃的大多数性质是由它们组装的结晶顺序的分数和类型决定的，这是支化含量和分布的函数。商业聚烯烃在链长和支化分布上过于复杂，不能产生链结构和性能之间的基本关系。在拟议的工作中，通过精确控制支化分布合成的聚乙烯和聚丙烯，无论是以精确的规则间距还是随机放置，都将作为建立基本行为的模型进行研究。特别强调了结晶动力学的作用，因为它与加工速度有关，在组装的晶体类型中。用模型系统预测了不同对称度的结晶，从而为开发新的聚烯烃带来了机会，其中聚合物的一级结构可以被操纵来控制物理性质。这项基础研究还旨在为研究生和本科生提供学习机会，其中许多人是少数族裔。

TECHNICAL SUMMARYResearch is proposed to advance knowledge of the interplay between chain microstructure, phase structure, crystallization kinetics and morphology of non-oriented bulk crystallized polyolefins. The aim is to understand this interplay using well-characterized systems that serve as models to predict the behavior of more complex commercial systems. Molecules could then be tailored with unique crystalline morphologies and properties. We seek to understand from first principles the role of crystallization kinetics on the development of the ultimate crystalline state. Of interest is the effect of undercooling on nucleus size, nature of folding when enabled, and impact in packing of sequence-specific macromolecules. Using polyethylene-based molecules with exquisite control in halogen substitution as model systems to predict kinetically controlled polymorphic transitions, further insights into primary chain deposition and subsequent arrangements are sought as they relate to classical and novel views of the path to polymer crystallization. In blends of metallocene-made poly(propylene) and higher alpha-olefin random copolymers, the role of sequence length distribution in polymorphic behavior and the crystalline phase structure that evolves will be addressed for a wide range of compositions.NON- TECHNICAL SUMMARYThe main proposed work involves the two leading commercial polyolefins, polyethylenes and polypropylenes. As they comprise over half of the annual production of all synthetic polymers, any improvement in the product, either by branching architecture, rate of processing, or judicious component blending will lead to a significant impact in the US and world economy. Most properties of these polyolefins are directed by the fraction and type of crystalline order that they assemble, which is a function of branching content and distribution. Commercial polyolefins are too complex in chain length and branching distributions to generate fundamental relations between chain-structure and properties. In the work proposed, polyethylenes and polypropylenes synthesized with exquisite control of branching distribution, either at a precise regular spacing or randomly placed will be studied as models to establish fundamental behaviors. Special emphasis is given to the role of crystallization kinetics, as it relates to processing rate, in the type of crystals assembled. Crystals with different degrees of symmetry are predicted with the model systems, thus bringing the opportunity to develop new polyolefins in which polymer primary structure can be manipulated to control physical properties. This fundamental research is also aimed to provide learning opportunities for both graduate and undergraduate students, many of them minority.