Heterogeneity in composition and dynamics in supercooled branched ionomers

Ionomers are useful in a wide range of applications including shape-memory materials, anti-microbial surfaces, and membranes for fuel cells. Cycled thermal treatment of a family of poly (3-sulfopropylmethacrylate-ran-methyl methacrylate) ionomers with different charge fractions shows a broadening glass transition range, which suggests compositional heterogeneity present in these systems. Using coarse-grained models and simulations, we characterize the thermal behaviors of these ionomers, and correlate them with the non-uniformity of the spatial distribution of monomer composition. We also examine the correlation between polymer dynamics during liquid-supercooled and supercooled-glass transitions and the ionomer charge fraction and side chain length. The findings offer insight into the convoluting interplay between key factors such as long-range Coulombic interactions in condensed phases, and the conformational entropy of the branched polymers and of the side chains.