Thermo-optical insights into the thermo-mechanical behaviour of dynamic polymer networks

Dr. Andreas Klingler, Leibniz-Institut für Verbundwerkstoffe GmbH, Kaiserslautern

Vitrimers, or more generally dynamic polymer networks, can reversibly change their phase state from a viscoelastic network structure with eternal character to a flowable state. This often temperature-controlled property transition is of particular interest, as it imparts certain reshaping and repair capabilities to these materials despite their covalent network bonds. However, the clarification and classification of the necessarily occurring phase transition from a viscoelastic solid to a flowable state due to dynamic covalent bond exchange requires further attention, as a correspondingly characteristic anomaly remains hidden in classical susceptibilities, such as the specific heat capacity.

In this talk, the phase transition behaviour of dynamic polymer networks will be first discussed from the perspective of dynamic thermal volume expansion. Since this property directly couples to the anharmonic molecular interaction potential, it is particularly suitable for studying solid-liquid phase and glass transitions. The rather new method of temperature-modulated optical refractometry (TMOR) used for this purpose provides simultaneously indirect insights into another key indicator for phase transitions: the shear relaxation behaviour.

Using selected model vitrimer systems, this coupled perspective of dynamic thermal volume expansion and shear relaxation will be discussed with regard to the property profile and the phase transition behaviour of dynamic polymer networks.