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

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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.