Correlation of molecular polymer properties with application properties of closed-cell foams based on self-synthesized model systems

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Polymer foams exhibit unique physical, mechanical and thermal properties. Therefore, the areas of application are very diverse, such as in thermal insulation, lightweight construction in general, and automotive parts in particular. The cell structure of polymeric foams, and thus their suitability for a specific application, is primarily determined by the interaction of technical process parameters and the molecular properties of the polymers or the resulting rheological properties of the polymer melt. Most studies in the literature refer to foaming techniques and process conditions. Only a few studies address the influence of polymer molecular properties. However, they are often based on industrial samples of an unknown topology or do not separate correlated effects from topology and crystallinity. A clear differentiation of the impact of topology has not been possible so far. Therefore, the overarching goal of this application is to understand the correlation of three key molecular polymer properties on the cellular structure and the resulting application properties of the resulting polymer foam, e.g. density, mechanical solid state properties, and thermal insulation capability. Tailor-made amorphous model polymers will allow us to study the influence of individual parameters separately, focusing on three different aspects: 1) Topology determines the shear and extensional rheological properties of the polymer melt and, thus, the expansion process. By systematically varying the topology, we will study the influence of rheological properties such as shear viscosity, extensional viscosity, and strain hardening behavior. 2) Fixation: Foam stabilization is determined by the mobility of the polymers and the type and proportion of the blowing agent. Specially synthesized homopolymers with varying glass transition temperature Tg but identical blowing agent solubility will be used to separate different influences. 3) Nucleation: phase-separating block copolymers exhibit intrinsic nucleation superior to homopolymers. By synthesizing systematically varied block copolymers, we will study the effect of heterogeneity of blowing agent solubility and the limitation of chain mobility by phase boundaries. The foams produced will be characterized by solid-state mechanical properties and imaging methods. The obtained knowledge will be incorporated into the molecular properties of the model systems in a circular process until the best possible understanding of the correlation of the molecular properties with the cellular structure and the application properties of the foams are achieved. The knowledge gained in the application should make it possible to directly determine the best possible polymer properties for a planned specific application of the foam, thus significantly simplifying the application-specific adaptation of the manufacturing process.