BLOCK-COPOLYMER IONOMERS - SOLUTION BEHAVIOR OF LIGHTLY SULFONATED POLYSTYRENE-B-POLY(TERT-BUTYLSTYRENE) IN POLAR-SOLVENT

Light scattering experiments were performed to study the structure and dynamics of block copolymer ionomers in polar solvent. Two lightly sulfonated polystyrene-b-poly(tert-butylstyrene)copolymers in the sodium form with a sulfonation level of 5.8 and 12.0 mol % dissolved in N,N-dimethylacetamide were studied at 25, 45, and 60-degrees-C in the dilute-solution regime. A polyelectrolyte-like solution behavior was observed. Due to the repulsive electrostatic interactions between like charges, the scattered intensities monitored were greatly reduced as compared with those of the unmodified diblock copolymer. In particular, a characteristic bimodal relaxation mode was observed on block ionomer solutions in strong contrast to the single-exponential decay found for the parent (neutral) copolymer solutions. Both the free-particle diffusion coefficient and the macroscopic self-diffusion coefficient as a function of temperature and concentration were determined and discussed. It seems that at 45 and 60-degrees-C charged monomolecular micelles are formed, whereas charged polymolecular aggregates would exist at room temperature arising from the delicate balance between the aggregation tendency and the solvent affinity.