Synthetic hydrogels. Part 8.–Physicochemical properties of N,N-dimethylacrylamide semi-interpenetrating polymer network hydrogels

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Abstract
The physicochemical properties of a range of semi-interpenetrating polymer networks (semi-IPNs) based on N,N-dimethylacrylamide and carbon backbone polymers containing pendant ester groups have been investigated. By varying the structure of the interpenetrant, the effects of factors such as the glass-transition temperature, molecular weight and compatability on the water-binding, surface and mechanical properties were examined. Discontinuities in both water-binding and mechanical properties versus composition curves were associated with phase changes in the semi-IPNs, as revealed by changes in optical properties. This effect was more pronounced in semi-IPNs with poly(methyl methacrylate) rather than poly(vinyl acetate) as the interpenetrant. The surface energies of the all hydrated semi-IPNs were lower than those associated with conventional copolymers; however, the mechanical properties, particularly the initial modulus of the NNDMA–PMMA semi-IPNs were dramatically improved.