Viscoelastic and Ultimate Behaviour of Swollen Poly (2-hydroxyethyl methacrylate) Networks Filled with Poly (2-hydroxyethyl methacrylate) in the Rubbery Region

Composite systems of the crosslinked and soluble poly(2-hydroxyethyl methacrylate) (PHEMA) matrix with various contents of crosslinked PHEMA particles containing 0.4, 1.0 and 20.0 wt. percent ethylenedimethacrylate as the crosslinking agent were prepared. Stress relaxations at the elongation λ = 1.1, stress-strain curves, Poisson's ratios, the degree of swelling and ultimate characteristics of samples swollen in water at 25°C were measured. With increasing filler content the time effects in the systems and the stress-at-break σb, and strain-at-break, σ b , also increase; these results corroborate the viscoelastic concept of the ultimate behaviour. An agreement was found between the experimentally determined course of the initial modulus G 0 and that predicted by Van der Poel as a function of the volume fraction of filler νf only for those systems in which the content of the crosslinking agent in the filler is smaller than in the matrix; systems with a higher content of the crosslinking agent in the filler than in the matrix require νf∗ = 3νf to fit the theory. Water present during the formation of filled systems preferentially swells the filler particles and reduces the polymerfiller interaction, which has a negative effect on the modulus G0 and on σb and ∊b.