Influence of Trimethylsilyl Side Groups on the Molecular Mobility and Charge Transport in Highly Permeable Glassy Polynorbornenes

Superglassy polymers with a large fractional free volume have emerged as novel materials with a broad range of applications, especially in the field of membrane separations. Highly permeable addition-type substituted polynorbornenes with high thermal resistance and chemical stability are among the most promising materials. The major obstacle for extending the practical membrane application is their strong tendency to physical aging, leading to a partial decline in their superior transport performance over time. In the present study, broadband dielectric spectroscopy with complementary X-ray scattering techniques were employed to reveal changes in microporous structure, molecular mobility, and conductivity by systematic comparison of two polynorbornenes with different numbers of trimethylsilyl side groups. Their response upon heating (aging) was compared in terms of structure, dynamics, and charge transport behavior. Furthermore, a detailed analysis of the observed Maxwell–Wagner–Sillars polarization at internal interfaces provides unique information about the microporous structure in the solid films. The knowledge obtained from the experiments will guide and unlock potential in synthesizing addition-type polynorbornenes with versatile properties.