Probing the glass transition and dynamic structural relaxation of polyzwitterions using fast scanning calorimetry*

Polyzwitterions are polymers with side groups that contain a covalently linked anion and cation. Depending upon side chain structure, this can lead to high glass transition temperatures, occurring near the onset of degradation. In this study we are using fast scanning calorimetry to investigate how different chemical structures in the side-group alter the glass transition (T_g) of polyzwitterions. A series of six sulfobetaine polyzwitterions were synthesized, each with a unique chemical modification of the side chain. T_g could not be observed prior to degradation in four of the polymers using conventional slow scan DSC. Using fast scanning calorimetry, degradation was avoided by heating and cooling at 2000 K/s which allowed the first measurement of T_g in these materials. We found that all six polymers have a T_g of 200 ^oC or greater depending on the specific side groups. Measurement of the fictive temperature (T_f) on heating at 2000 K/s after cooling samples at different rates allowed determination of the dynamic fragility. We found that the polyzwitterions are moderately strong polymer glass formers, indicating the significance of the unique ionic structure of these polymers to their structural relaxation.