Preparation and thermal characterization of the glass transition temperatures of sulfonated polystyrene-metal ionomers

The glass transition temperatures and heat capacity changes in the transition region are reported for six sulfonated linear polystyrenes in the hydrogen form, H-SPS, in the 3.4–20.1 mol % sulfonation range and 76 metal SPS ionomers in the 3.4–12.8 mol % range. The metals are those which interact predominantly ionically and include +1, +2, and +3 ions of the alkali metal, alkaline earth, and rare earth (lanthanide) series. The results show the effect of H₂O or coordinating ligands on glass transition temperatures (T_g) and the importance of eliminating it to obtaining reproducible values for T_g and ΔC_p. The T_g values of dry M-SPS ionomers depend only on the sulfonation level despite wide variation in metal ion charge and size. The variation of ΔC_p with sulfonation level is interpreted as showing that at high levels a few unsulfonated styrene units adjacent to sulfonated ones are constrained, presumably by clustering, from participation in the polystyrene-like cooperative rearrangements in the transition region.