Preparation and association behavior of diblock copolymer ionomers based on poly(styrene-b-ethylene-co-propylene)

Two kinds of diblock ionomer were prepared by carboxylating and sulfonating the polystyrene (PS) block of a commercial product of poly (styrene-block-ethylene-co-propylene) (SEP). The PS block was partially carboxylated via a mild Friedel–Crafts acetylation and a subsequent haloform oxidation. The carboxylation only slightly changed the molecular weight distribution of the SEP at low carboxylation levels typical for ionomers. Acetyl sulfate was used as the sulfonating agent for sulfonation. Both carboxylated SEP and sulfonated SEP ionomers with either lithium or zinc as counterions exhibit increased decomposition temperature and higher Tg of the PS blocks compared with their base resin as a result of intermolecular association due to the interactions of ionic groups. The ionomers show apparently increased viscosity than SEP. The data indicate that the sulfonate groups have stronger ability of association than the corresponding carboxylate groups, while zinc ions stronger than lithium ions. A combination of static and dynamic light scattering directly provides semi-quantitative information of association of the diblock ionomers, e.g., for the ionomers with functionality of 5.3 mol%, the association number was found to range from 8 to 17 depending on the nature of the cationic and anionic groups incorporated.