Glass-Forming Ability of Polyzwitterions

Abstract

The glass-forming ability of a series of specially synthesized polyzwitterions was studied using fast scanning calorimetry (FSC). Polyzwitterions include those based on the sulfobetaine moiety: sulfobetaine acrylate, ethyl sulfobetaine methacrylate, sulfobetaine vinylimidazole, sulfobetaine 4-vinylpyridine, sulfobetaine methacrylate, and sulfobetaine methacrylamide. FSC was used to investigate the dynamic fragility over a large range of cooling rates, 10-4000 K/s, minimizing thermal degradation of the polyzwitterions. The rate dependence of the limiting fictive temperatures (Tf) was measured and fit to the Williams-Landel-Ferry model, from which the polyzwitterion dynamic fragility was determined for the first time. Dynamic fragility was low, ranging from 41 to 110, depending on the underlying chemical structure, which allows classification of this series of polyzwitterions as moderate to relatively strong polymeric glass formers. Their high glass transition temperatures combined with low fragilities indicates that polyzwitterions are unique among polymeric glass formers. This behavior arises from the formation of inter- and intrachain dipole-dipole cross-links which causes more dense molecular packing and cohesion.