Dynamic Properties of Block Ionomer Complexes with Polyion Complex Cores

Abstract

Reactions of polyion coupling and interchange were investigated using fluorescence quenching techniques in three systems: (1) soluble nonstoichiometric interpolyelectrolyte complex (IPEC) of poly(methacrylic acid) (PMA) and poly(N-ethyl-4-vinylpyridinium bromide) (PEVP), (2) block ionomer complex (BIC) of poly(ethylene oxide)-b-poly(methacrylic acid) copolymer (PEO-b-PMA) and PEVP, and (3) BIC of cross-linked ionic core PEO-b-PMA (#PEO-b-PMA) and PEVP. All measurements were done at the excess of the polyanion (base-molar ratio [PEVP]/[PMA] = 0.2). Rapid polyion coupling was observed following mixing the components in all three systems. However, unexpectedly, the rate of the polyion exchange and substitution reactions increased in the following order: IPEC < BIC < core cross-linked BIC. We posit that the free polyanion chain approaching and interpenetrating the polyion complex experiences greater electrostatic repulsion of the excess PMA units exposed at the IPEC surface compared to the PMA units hidden in the core of BIC. This may slow down the transfer of the PEVP chain from the IPEC to the free polyanion. Evidently, the steric repulsion of PEO chains in the BIC shell does not hinder the association of the reacting species or interpenetration and electrostatic coupling of the polyion chains.