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

在这个项目中，我们想要研究定义明确的模型聚合物在静态和流动条件下的结晶行为，包括其分子动力学、纳米尺度的形态和流变性。为了能够分析相关性和结构-性质-关系，我们将充分利用联用流变学技术，在进行大量流变测试的同时，表征原位分子动力学(RheoNMR)和纳米级形态(RheoSAXS/WAXS)。我们之前的发现受到商业上可获得的半结晶聚合物的广泛分子量分布的限制，特别是在聚乙烯(高多分散性)的情况下。在这里，我们希望通过催化聚合技术来合成具有窄分子量分布和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质和分子参数之间的关系，这些参数涉及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构建。我们的目的是了解内部参数(分子量分布、立体规律性)和外部参数(温度、剪切)对聚合物结晶过程的影响。根据外加剪切速率、剪切持续时间和总应变，将为每个模型系统确定诱发形核和形成行形核结构所需的关键参数，并将与结构参数相关联。通过将这些结果与聚合物动力学模型进行比较，我们将对流动诱导聚合物结晶背后的机理有一个更深刻的理解。

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.