Understanding the Roles of Mesh Size, Tg, and Segmental Dynamics on Probe Diffusion in Dense Polymer Networks

Butyl acrylate polymer networks were synthesized to understand the effect of permanent cross-links on large, anisotropic dye diffusion. The average degree of polymerization between cross-links (N-x) was decreased from 92 to 2, leading to a 2 order of magnitude decrease in the probe translational diffusion coefficient (D). The mesh size (a(x)) was determined from Young's modulus, and D showed a weakening single exponential decay dependence on the ratio of the probe long axis (d(long)) to a(x) with increasing experimental temperature (T-0). Cross-linking led to a significant increase in the glass transition temperature (T-g) of the networks and its breadth determined by both calorimetry and dielectric spectroscopy. Segmental relaxation times and inverse diffusion coefficients exhibited weakening single exponential relationships with d(long)/a(x) and T-g/T-0 at lower measurement temperatures. These results provide new insights regarding the effect of covalent cross-links on probe diffusion necessary for the design and development of separation membranes.