Thermal and structural studies of polyzwitterion/salt complexes

The thermal and structural properties of five amorphous polyzwitterion (PZI)/LiCl salt complexes were investigated using differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). Poly(sulfobetaine methacrylate), PSBMA, poly(sulfobetaine acrylate), PSBA, poly(ethyl sulfobetaine methacrylate), PESBMA, poly(ethyl sulfobetaine acrylate), PESBA, and poly(sulfobetaine methacylamide), PSBMAm, were synthesized with variations in the sidechain and backbone. Here, we investigate the effects of LiCl salt addition to PZI solution cast films; LiCl composition in the complexes varied from about 0.06 to 1.65 mol.%. In PZI without added salt, intra- and inter-molecular crosslinks are formed between zwitterionic moieties, leading to an increase in the glass transition temperature (T_g) and a decrease in the heat capacity increment at T_g. As the LiCl content increases, crosslinking is disrupted leading to a decrease in T_g, and a decrease in the interatomic spacing as observed using WAXS. For the composition range we studied, addition of LiCl results in an increase of the molecular mobility through reduction of intra- and inter-chain crosslinking.