Hydrogen Bonding Effect on Probe Diffusion in Semidilute Polymer Solutions:  Polymer Chain Structure Dependence

The diffusivity of 4-[[4‘-(dimethylamino)phenyl]azo]benzoic acid (p-MR) in poly(methyl methacrylate) (PMMA)/toluene solution was found to be much lower than in polystyrene solution due to the hydrogen bonding interaction between the diffusant and the polymer matrix. In order to study the effect of the H-bonding interaction in a quantitative manner, the content of MMA units in the polymer matrix capable of H-bonding with p-MR was varied using mixtures of polystyrene (PS) and PMMA as well as PS/PMMA random and diblock copolymers. In the mixture or diblock copolymer systems, the diffusion behavior of the probe could be well represented by a phenomenological model which assumes the additivity of the diffusional activation barriers due to hydrodynamic interaction and H-bonding interaction. On the other hand, we observed far more effective H-bonding in random copolymers than in mixtures or in block copolymers. The diffusivity of p-MR in a solution of random copolymers with MMA content of 40% or higher was found to be similar to pure PMMA. This peculiar behavior of p-MR diffusion in random copolymers may reflect the difference in binding efficiency of the copolymers and in the microscopic environment for the diffusion path of p-MR.