Study of the crystallization behavior of model polyolefins under quiescent and flow conditions using hyphenated techniques of rheology, NMR, and X-ray scattering

在拟议的项目中，我们要研究的结晶行为定义明确的模型聚合物在静态和流动条件下，其分子动力学，纳米尺度上的形态，和流变流动行为。为了能够分析相关性和结构-性能-关系，我们将充分利用联用流变技术，该技术被开发用于表征原位分子动力学（RheoNMR）和纳米级形态（RheoSAXS/WAXS），同时进行大量的流变测试。我们以前的研究结果受到市售半结晶聚合物的宽分子量分布的限制，特别是在聚乙烯（高多分散性）的情况下。本论文的目的是利用催化聚合技术合成窄分子量分布、不同平均分子量的模型聚烯烃。我们的目标是确定宏观材料性能和分子参数之间的相关性，相对于静态结晶过程中的硬化行为和流动诱导结晶过程中的结构建设。我们的目标是实现内部（分子量分布，立体规整性）和外部参数（温度，剪切）对聚合物结晶过程的影响的理解。对于每个模型系统，将确定诱导成核和形成行成核结构所需的施加剪切速率、剪切持续时间和总应变方面的关键参数，并将其与结构参数相关联。通过将这些结果与聚合物动力学模型进行比较，我们将深入了解流动诱导聚合物结晶的机理。

In the proposed project, we want to study the crystallization behavior of well-defined model polymers under quiescent and flow conditions with respect to its molecular dynamics, the morphology on the nanometer scale, and the rheological flow behavior. To be able to analyze correlations and structure-property-relationships we will make full use of hyphenated rheology techniques that were developed to characterize in-situ molecular dynamics (RheoNMR) and nanoscale morphology (RheoSAXS/WAXS) while conducting a multitude of rheological tests. Our previous findings were limited by the broad molecular weight distributions of commercially available semi-crystalline polymers, especially in the case of polyethylene (high polydispersity). Here, we want to synthesize model polyolefins with narrow molecular weight distributions and different average molecular weights by using catalytic polymerization techniques. Our goal is to identify correlations between the macroscopic material properties and molecular parameters with respect to the hardening behavior during quiescent crystallization and the structural buildup during flow-induced crystallization. We aim at achieving an understanding of the influence of internal (molecular weight distribution, stereo regularity) and external parameters (temperature, shear) on the process of polymer crystallization. The critical parameters in terms of applied shear rate, shear duration, and total strain that are needed to induce nucleation and to form row-nucleated structures will be determined for each model system and will be correlated with the structural parameters. By comparing those results with models for the dynamics of polymers, we will achieve a deep understanding of the mechanism behind flow-induced polymer crystallization.