FRG: GOALI: Collaborative Research: The Role of Polymer Molecular Architecture in Controlling Morphology in Quiescent and Flow-Induced Crystallization

技术概述：该提案将弗吉尼亚大学、康奈尔大学和佛罗里达州立大学的学术研究小组与埃克森美孚研究与工程公司的一位领先的聚烯烃工业科学家联合起来。研究重点是开发新型聚丙烯合成化学，探索半结晶聚合物在静态和流动诱导结晶过程中成核和生长的基本物理现象。具体来说，pi将使用分支结构作为控制成核的工具，从而操纵最终的晶体形态和宏观材料特性。为实现这一目标而组建的团队精通新型聚烯烃合成、结晶动力学和结构表征、流变学和流动诱导结晶以及工业聚合物加工。模型等规聚丙烯（iPP）材料，包括窄分子量分布线性，星形，H-和梳状聚合物，将合成具有精确控制的立体规则和分支点的位置。静态结晶实验将主要寻求确定：(1)由于分支而增加的链不规则性对均聚物样品中晶体组织水平和α相和γ相相对含量的影响；(2)增强线性链共混物成核的分支结构类型和构象。线性和支化iPP共混物的流动诱导结晶将试图确定：(1)在固定的最长松弛时间内，支化如何影响结晶动力学、成核密度、结晶度和晶体结构；(2)分子结构是否改变了局部节段取向以促进成核；(3)多态和形态如何取决于臂的数量（星形）、支链与主链分子量的比例（h -聚合物）和分支点的数量（梳）。非技术总结美国每年生产超过4300万吨热塑性树脂，估计市场价值超过650亿美元。许多处理以特别的方式执行，没有建模或连贯混合策略的好处。由于原材料通常不可再生，加工过程中的废物对环境产生重大影响。此外，更好地控制结晶度和晶体形态的能力将导致更好的薄膜，更轻的零件，并且由于材料性能的扩展，也将廉价的PP材料注入新的应用领域。通过在定义良好的材料系统上提供静态和流动诱导结晶数据，预计这项工作将产生允许定量预测半晶体形态的理论工具。化学和化学工程专业的学生不仅可以接触到现代聚合物合成和表征、流变学和材料表征技术（例如，x射线散射、双折射、光学和透射电子显微镜），而且还可以参与埃克森美孚的工业研究经验。pi还将结合他们不同的才能和观点，组建一个K12“塑料”教育计划，并在各自的社区采用。pi也有在他们的研究工作中纳入代表性不足的群体的记录（例如，来自加纳和巴拿马的本科生以及一些女性本科生、研究生和博士后）。此外，FAMU-FSU工程学院是FAMU和FSU的联合管理项目，FAMU是一所历史悠久的黑人学院和大学，FSU有40%的少数民族和25%的女性入学率，许多非裔美国本科生在该机构的PI实验室进行了本科研究。

TECHNICAL SUMMARYThis proposal unites academic research groups at the University of Virginia, Cornell University, and Florida State University with a leading polyolefin industrial scientist at ExxonMobil Research and Engineering Corporation. The research focuses on the development of novel polypropylene synthetic chemistry and an exploration of the fundamental physical phenomena underlying nucleation and growth in quiescent and flow-induced crystallization of semicrystalline polymers. Specifically, the PIs will use branching architecture as a tool to control nucleation and thereby manipulate the final crystalline morphology and macroscopic material properties.The team assembled to achieve this goal is skilled in novel polyolefin synthesis, crystallization kinetics and structural characterization, rheology and flow-induced crystallization, and industrial polymer processing. Model isotactic polypropylene (iPP) materials, including narrow molecular weight distribution linear, star, H-, and comb polymers, will be synthesized with precisely controlled stereoregularity and location of branch points. Quiescent crystallization experiments will principally seek to ascertain: (1) the influence of increasing chain irregularity due to branching on the level of crystalline organization and relative content of the alpha and gamma phases in homopolymer samples; and (2) the type and conformation of branching architecture that enhances nucleation in blends with linear chains.Flow-induced crystallization of linear and branched iPP blends will seek to determine: (1) how crystallization kinetics, nucleation density, degree of crystallinity, and crystalline structure are influenced by branching for fixed longest relaxation time; (2) if molecular architecture alters the local segmental orientation to promote nucleation; and (3) how polymorphism and morphology depend upon the number of arms (stars), ratio of branch to main chain molecular weight (H-polymers), and number of branch points (combs). NON-TECHNICAL SUMMARYOver 43 million tons of thermoplastic resins are produced in the U.S. each year with an estimated market value of over $65 billion. Much processing is performed in an ad hoc manner without the benefit of modeling or coherent blending strategies. Since the raw materials are often not renewable, waste in processing has a significant environmental impact. Moreover, the ability to exert better control over crystallinity and crystalline morphology will lead to better films, lighter weight parts, and also inject inexpensive PP materials into novel applications due to extended material properties. By providing quiescent and flow-induced crystallization data on well-defined material systems, theoretical tools allowing quantitative predictions of semicrystalline morphology are expected to result from this work. Students in Chemistry and Chemical Engineering will be not only be exposed to modern polymer synthesis and characterization, rheology, and material characterization techniques (e.g., X-ray scattering, birefringence, optical and transmission electron microscopy), but they will also be able to participate in industrial research experiences at ExxonMobil. The PIs will also combine their diverse talents and perspectives to assemble a K12 educational program on "Plastics" to be adopted in their respective communities. The PIs also have a record of including underrepresented groups in their research efforts (e.g., undergraduates from Ghana and Panama and several female undergraduates, graduates, and postdocs). Additionally, the FAMU-FSU College of Engineering is a jointly managed program of FAMU, a historically black college and university, and FSU with 40% minority and 25% female enrollment, and numerous African-American undergraduates have conducted undergraduate research in the laboratory of the PI at that institution.