Response of Ionic co Polymers to Tuning Solution Dielectrics

Ionic cluster formation often drives assembly of ionizable co-polymers in solutions, where response to any stimuli is a balance of the behavior polymers with significantly different characteristics. Here, small angle neutron scattering (SANS) was used to follow the response of assemblies of a symmetric pentablock copolymer, that consists of a randomly sulfonated polystyrene (sPS) centers with sulfonation fractions varied from neutral to ionomer to the polyelectrolyte regime. This block is symmetrically tethered to polyethylene-r-propylene block, terminated by poly (t-butyl styrene). SANS measurements were carried out as the solvent polarity was manipulated through addition of propanol to cyclohexane, increasing the dielectric constant. We find that regardless of sulfonation fraction, the propanol penetrates and swells the ionic core, decreasing the cohesiveness of the ionic clusters. The polymers however remain assembled as the corona collapses with increasing propanol, but assemblies change their shape from spherical to elliptical. The assemblies that were initially formed by segregation of the ionic blocks are now held together by the collapse of the hydrophobic blocks.