Development and optimization of crystallization-inhibited polymer networks for strain-induced switching from entropy- to energy-elastic behavior

• Applicant: Professor Dr. Jörg Tiller
• Subject Area: Polymer Materials ; Synthesis and Properties of Functional Materials
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 535472234

The aim of the current research project is to develop a novel concept for the synthesis of polymer networks that remain amorphous up to a certain limit temperature above room temperature, crystallize exclusively under strain below this temperature, and thus have enormous shock and energy absorption capabilities. To this end, blends of an amorphous and a crystallizable polymer with significant partial miscibility were cross-linked. The basic suitability of this concept for the realization of polymers with shock and energy absorption capability has already been demonstrated in the project using PVDF/PEtOx and PVDF/PVAc networks. During thermomechanical characterization and initial drop tests, it was found that slight crystallization of the co-networks does not necessarily lead to a loss of shock and energy absorption capacity and that further thermal crystallization is self-inhibiting under certain conditions. This self-inhibition effect is probably due to the fact that, under certain conditions, the amorphous phase is unable to compensate for the crystallization-induced local PVDF depletion around the crystals, resulting in the formation of a Tg barrier, which is capable of inhibiting uncontrolled thermal crystallization at temperatures up to the level of this barrier. During the one-year project extension, the influencing parameters of the observed self-inhibition of thermal crystallization of PVDF in PVDF/PVAc networks will be identified in order to exploit them for tailoring the morphology and thus the Tg barrier. The aim is to inhibit any further thermal crystallization up to a limit temperature above room or application temperature of the shock and energy-absorbing PVDF/PVAc network by specifically growing a few crystals, so that even after prolonged storage at temperatures below this limit temperature, the shock and energy absorption capacity is not lost.

• DFG Programme: Research Grants
• Co-Investigator: Privatdozent Dr. Frank Katzenberg