Characterization of anionic/cationic sequential IPNs. II. Studies of swelling, modulus, and alternate phase staining with CsF and LiI

Abstract

AbstractAnionic/cationic interpenetrating polymer networks (IPNs) were synthesized by sequential polymerization from crosslinked polystyrene, PS, as polymer I and crosslinked poly(4‐vinyl pyridine), P(4‐VP), as polymer II. Ionomeric substitution of the two networks was based on sulfonation and quaternization of the phenyl and pyridine rings, respectively. The swelling, morphological, and dynamic mechanical behavior of ionomeric and unsubstituted IPNs was explored as a function of overall IPN composition. A theoretical analysis of the unsubstituted IPNs via the Thiele–Cohen equation showed that essentially no additional physical or chemical crosslinks were developed in the swollen state. Modulus studies showed that network I tends to dominate the mechanical properties in the bulk state. Swelling studies on the ionomeric IPNs as a function of pH demonstrated a complex change in behavior with the addition of NaCl, possibly due to an ionic screening effect. Electron microscopy involved alternate staining of the anionic and cationic phases using CsF and Lil and showed a two‐phase structure, with the possibility of additional phases within phases due to separation of the ionomeric components. Comparison of the two staining techniques yielded strong evidence of a positive/negative–negative/positive phase contrast, depending on the phase being stained. In each case, domains were less than 100 nm (1000 Å), with the domain size decreasing as the P(4‐VP) content increased. Also, a phase inversion appeared to occur between 50 and 80% P(4‐VP). The dynamic mechanical studies supported the two‐phase morphology and gave evidence of significant molecular mixing between the phases.