Molecular Aspects of Flow Effects on Crystallization in iPP

技术描述：半结晶聚合物占所有合成聚合物年产量的三分之二以上，并正在复兴之中，因为最近开发的茂金属催化剂通过控制大分子结构获得了最终性能的新组合。本研究使用新型仪器和模型聚合物来发现半晶体纳米结构自组装的分子基础，特别是在流动的影响下。在接下来的三年中，将测量作为聚合物分子特征、温度和应力的函数的丝状前驱体的轴向传播速度。将使用定义好的长度和分布的聚合物来指定熔体中的链动态。双折射和同步辐射X射线测量将跟踪取向前驱体的形成和晶体的生长。为了实现合理设计聚烯烃分子结构的目标，实验观察将指导理论和建模方面的进展。具体地说，与韩美杰和格瑞特·彼得斯的合作研究将应用实验结果，将分子描述符纳入流动诱导结晶的可恢复应变模型。智力价值：加工对结晶动力学和形态产生深刻影响的基本基础是熔融链的构象动力学、变形熔体成核的动力学和各向异性及其对后续结晶动力学和形态的影响的相互作用。本研究采用综合实验的方法来揭示分子属性、流动行为和结晶之间的关系。为了将学术实验扩展到技术设计工具，关于分子结构作用的新知识被转化为预测建模方面的进展。在基础科学方面，这个项目阐明了加工影响聚合物结构发展的基本机制。在工业实践方面，相关工艺的基本知识被用于开发从分子到宏观性质的预测模型，这些模型有可能彻底改变半结晶聚合物的大分子和工艺设计。广泛影响：技术转让活动包括与宝洁公司持续合作，开发用于非织造布的新型双峰树脂。从事该项目的博士研究员通过与工业界和国际科学家的密切互动，丰富了他们的教育经验。此外，DMR支持促进持续的外展活动：Kornfield为以中学女生为对象的Sally Ride科学节做出贡献，并参加加州理工学院工程预览，向未被充分代表的本科生提供有关研究生学习的信息。

Technical Description: Semicrystalline polymers comprise over two-thirds of the annual production of all synthetic polymers and are in the midst of a renaissance, as recently developed metallocene catalysts give access to new combinations of final properties through control of macromolecular structure. The present research uses novel instrumentation and model polymers to discover the molecular basis of self-assembly of the semicrystalline nanostructure, particularly under the influence of flow. During the next three years the axial propagation velocity of threadlike precursors will be measured as a function of the molecular characteristics of the polymer, temperature and stress. Polymers of well-defined length and distribution will be used to specify the chain dynamics in the melt. Birefringence and synchrotron x-ray measurements will track the formation of oriented precursors and the growth of crystallites from them. Toward the goal of enabling rational design of the molecular structure of polyolefins, experimental observations will guide advances in theory and modeling. Specifically, collaborative research with Han Meijer and Gerrit Peters will apply experimental results to incorporate molecular descriptors into the recoverable strain model for flow-induced crystallization.Intellectual Merit: The fundamental basis of the profound effects of processing on crystallization kinetics and morphology is the interplay of the conformational dynamics of the molten chains, the kinetics and anisotropy of nucleation from a distorted melt, and their effects on the subsequent kinetics and morphology of crystallization. This research adopts a comprehensive experimental approach to reveal the connection between molecular attributes, flow behavior and crystallization. To extend academic experiments to technological design tools, new knowledge of the role of molecular structure is translated into advances in predictive modeling. In terms of basic science, this program elucidates the fundamental mechanism by which processing affects polymer structure development. In terms of industrial practice, fundamental knowledge of the processes involved is used to develop predictive models that bridge from molecules to macroscopic properties that have the potential to revolutionize macromolecular and process design of semicrystalline polymers.Broader Impacts: Technology transfer activities include ongoing collaboration with Procter and Gamble on the development of new bimodal resins for non-woven fabrics. The educational experience of the doctoral researcher engaged in the project is enriched by close interaction with industrial and international scientists. In addition, DMR support fosters ongoing outreach activities: Kornfield contributes to the Sally Ride Science Festival that targets middle-school girls and participates in the Caltech Engineering preview providing information on graduate studies to underrepresented undergraduates.