Molecular Aspects of Flow Effects on Crystallization in iPP

技术说明：半结晶聚合物占所有合成聚合物年产量的三分之二以上，并且正处于复兴之中，因为最近开发的茂金属催化剂通过控制大分子结构提供了最终性能的新组合。 本研究使用新的仪器和模型聚合物，发现半结晶纳米结构的自组装的分子基础，特别是在流动的影响下。 在接下来的三年中，将测量线状前体的轴向传播速度作为聚合物的分子特性、温度和应力的函数。 明确定义的长度和分布的聚合物将被用来指定在熔体中的链动力学。 双折射和同步加速器X射线测量将跟踪定向前体的形成和微晶的生长。 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的进展。 具体而言，与Han Meijer和Gerrit Peters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。加工对结晶动力学和形态的深刻影响的基本基础是熔融链的构象动力学、从扭曲熔体成核的动力学和各向异性、以及它们对随后的结晶动力学和形态的影响。 本研究采用综合实验方法，揭示分子属性、流动行为和结晶之间的联系。 为了将学术实验扩展到技术设计工具，将分子结构作用的新知识转化为预测建模的进展。 在基础科学方面，该计划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，所涉及的过程的基础知识被用来开发预测模型，从分子到宏观性能的桥梁，有可能彻底改变大分子和工艺设计的半结晶聚合物。更广泛的影响：技术转让活动包括正在进行的合作，与宝洁公司开发新的双峰树脂的非织造布。 从事该项目的博士研究员的教育经验通过与工业和国际科学家的密切互动而丰富。 此外，DMR支持促进正在进行的外联活动：康菲尔德有助于莎莉莱德科学节，目标是中学女生，并参加加州理工学院工程预览提供研究生学习的信息，以代表性不足的本科生。

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.