Physicomechanical and dielectric properties of magnesium and barium ionomers based on sulfonated maleated styrene-ethylene/butylene-styrene block copolymer

Ionomers, containing both carboxylate and sulfonate anions on the polymer b ackbone, based on metal cations like Mg+2 and Ba+2 were prepared by sulfona ting maleated styrene-ethylene/butylene-styrene block copolymer, hereafter referred to as m-SEBS, followed by its neutralization by metal acetates. In frared spectroscopic studies reveal that sulfonation reaction takes place i n the para position of the benzene rings of polystyrene blocks and metal sa lts are formed on neutralization of the precursor acids. Dynamic mechanical thermal analyses show that sulfonation causes increase in T-g of the rubbe ry phase of m-SEBS and decrease in tan delta at T-g of the hard phase, alon g with formation of a rubbery plateau. The changes become more pronounced o n neutralization of the sulfonated maleated SEES, and the effect is greater in the case of Ba salt. Dielectric thermal analyses (DETA) show that incor poration of ionic groups causes profound changes in the dielectric constant (epsilon') of m-SEBS. In addition to the low temperature glass-rubber tran sition, the plot of epsilon' vs, temperature shows occurrence of a high-tem perature transition, also known as the ionic transition. Activation energy for the dielectric relaxation could be determined on the basis of frequency dependence of the ionic transition temperature. Two values of the activati on energy for the dielectric relaxation refer to the presence of two types of ionic aggregates, namely multiplets and clusters. Incorporation of the i onic groups causes enhancement in stress-strain properties as well as reten tion of the properties at elevated temperatures (50 degrees and 75 degrees C), and the effect is more pronounced in the case of Ba ionomer. Although s ulfonated ionomers show greater strength than the carboxylated ionomers, th e sulfonated maleated ionomers show higher stress-strain properties in comp arison to both sulfonated and carboxylated ionomers. (C) 2000 John Wiley & Sons, Inc.