Effect of Chemical Crosslinks on Ultimate Tensile Properties of Water Swollen Poly(2-Hydroxyethyl Methacrylate) Gels

Abstract

Tensile properties were measured of poly(2-hydroxyethyl methacrylate), swollen with water to equilibrium and prepared in the presence of ethylene dimethacrylate as the crosslinking agent within the concentration range from c = 0.0855 to 5.65 × 10⁻⁴ mol crrr⁻³ and water as the diluent during polymerization up to the volume fraction of the polymer v₀ = 0.2. Tensile strength and strain-at-break were determined at 5°C and crosshead speed 10 mm s⁻¹, and also at 25°C and 1 mm s⁻¹. Both tensile strength and strain-at-break depended with good approximation on the effective crosslinking density only, irrespective of the crosslinking agent and diluent contents during polymerization. An exception occurs in heterogeneous systems polymerized in the presence of a large volume of water (v₀ < 0.6). The temperature and time dependences of the strength characterictics of samples having three different crosslinking densities were summarized in a universal failure envelope. The points pertaining to samples having the lowest crosslinking density (c = 0.085 × 10⁻⁴ mol cm⁻³) departed from the failure envelope towards larger deformations. This effect was explained in connection with the time and temperature dependence of the elasticity modulus of lightly crosslinked elastomers.