Model Polyelectrolyte Gels Synthesized by End-Linking of Tetra-Arm Polymers with Click Chemistry: Synthesis and Mechanical Properties

A series of poly(sodium acrylate) gels was synthesized via end-linking reaction between tetra-arm poly(tert-butyl acrylate)s by copper-catalyzed azidealkyne cycloaddition followed by deprotection of tert-butyl group and neutralization. Characterization of the gels using gravimetry, IR measurement, and stretching test revealed that they have only small amounts of sol fractions, dangling chains, and trapped entanglements. The relationship between polymer weight fraction (phi(e)) and shear modulus (G') at equilibrium swelling in saline was expressed as G' proportional to phi(2.5)(e). The power index (2.5) was comparable with the theoretical value for nonionic gels swollen in good solvents (2.3). The relationship between G' and phi(e) was superior to that of poly(sodium acrylate) gels synthesized by conventional radical copolymerization. The difference may be partly attributed to the difference in the ratio of chemical cross-links to trapped entanglements.