Deformational, swelling, and potentiometric behavior of ionized gels of 2‐hydroxyethyl methacrylate–methacrylic acid copolymers

Abstract

The deformational, swelling, and potentiometric behavior of ionized water‐swollen gels of 2‐hydroxyethyl methacrylate (HEMA)–methacrylic acid (MA) copolymers used in biomedical and separation applications was investigated. With increasing degrees of neutralization α, the swelling degree strongly increases and the modulus G_s decreases. For the copolymers with MA content ⩾ 30 mole‐%, the dependence of G_s on α passes through a minimum. Comparison of the results with the modified theory of rubber elasticity shows that the decrease in G_s at low concentrations of charges on the chain is controlled mainly by the degree of swelling. At higher α, both the finite extensibility of network chains, caused by a high degree of swelling, and electrostatic interactions contribute to G_s. The dependence of the interaction parameter χ on the volume fraction of polymer in the gel, v₂, is independent of α and closely resembles the dependence obtained for other hydrophilic polymers.