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 c arboxylation only slightly changed the molecular weight distribution of the SEP at low carboxylation levels typical for ionomers. Acetyl sulfate was u sed as the sulfonating agent for sulfonation. Both carboxylated SEP and sul fonated SEP ionomers with either lithium or zinc as counterions exhibit inc reased decomposition temperature and higher T-g of the PS blocks compared w ith their base resin as a result of intermolecular association due to the i nteractions of ionic groups. The ionomers show apparently increased viscosi ty than SEP. The data indicate that the sulfonate groups have stronger abil ity of association than the corresponding carboxylate groups, while zinc io ns stronger than lithium ions. A combination of static and dynamic light sc attering 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 n ature of the cationic and anionic groups incorporated. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.