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Molecular modeling study of sulfonated SIBS triblock copolymers

An important class of thermoplastic elastomers involves polystyrene and polyisobutylene blocks (SIBS). Sulfonated SIBS Triblock Copolymers (S-SIBS) are of particular interest because of potential applications for fuel cell and textile applications, where breathable, protective clothing is required. We have used multiscale modeling to gain an understanding of the static and dynamic properties of these polymer systems at detailed atomistic levels. Quantum chemistry tools were used to elucidate the bonding of water molecules and sulfonate groups. In addition, molecular dynamics was applied to calculate the polymer density at various levels of sulfonation. The structures of polymer with hydronium ions and also water were studied and the mechanism of water self-diffusion was proposed. It was found that with increase of water content the hydronium ions move further away from sulfonate groups. The self-diffusion coefficients of water were found to reproduce well experimental trends. Two different distributions of sulfonate groups were studied: one blocky and another perfectly dispersed. In the case of the blocky architecture, the water clusters are connected at a lower sulfonation level, leading to increased water diffusion coefficients as compared to the dispersed architecture.