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This research was undertaken to develop a better understanding of the relationships among the compositions, structures and properties of denture soft liners. Five butadiene-styrene-acrylic elastomers were prepared. They were prepared using 50% of powdered prepolymerized butadiene-styrene polymer combined with 50% of a methacrylate monomer (HMA or EHMA) plus varying amounts of initiator and crosslinker. The mixtures were gelled and processed conventionally. Specimens were then committed to dynamic mechanical analysis and water sorption. Dynamic mechanical analysis was performed over the temperature range 5–95°C at the rate of 2.5°C/min using a Perkin Elmer DMA-7 with 3 mm flat tip probe at 1 Hz. Wet and dry values for storage modulus (E') and damping factor (tan d) were determined at 37°C. Water sorption of these butadiene styrene elastomer-acrylic systems from solutions of varying concentrations was measured in order to establish the role of osmotic pressure. Diffusion coefficient (Dd) was determined from the desorption values. The relatively lower values of Dd observed in most highly concentrated solutions particularly 1 m sodium chloride and glucose may be interpreted as related to reduced water sorption from these solutions. Increasing crosslinking increased the modulus and decreased water sorption. Using hydrophobic EHMA instead of HMA reduced water uptake, reduced dry modulus and reduced the decrease in modulus caused by water sorption. Dynamic moduli and water sorption generally exceeded those of the commercial materials studied. For all experimental materials, water uptake from saline and glucose solutions confirmed that the diffusion process is osmotically driven.

A series of experimental soft lining materials has been produced using a butadiene/styrene copolymer with methacrylate monomers, and assessed in terms of their tensile properties. Three different methacrylate monomers, n-hexyl (HMA), ethyl hexyl (EHMA) and 1-tridecyl (TDMA), and two different initiators, benzoyl peroxide (BP) and lauryl peroxide (LP), were used. Other variables were copolymer/monomer ratio and level of cross-linking. Water sorption studies were also carried out on some of the materials, selected in terms of strength, on the pure copolymer (with and without partitioning agent) and on homopolymers of HMA and EHMA. Generally, the EHMA-based materials had the highest strengths and the TDMA the lowest. The highest tensile strength at 11.36±1.80 MPa was produced by the 50/50, LP initiated EHMA material with 1% cross-linking agent, which also had the lowest water uptake. There appeared to be a relationship between tensile strength and water uptake. Water uptake was found to be governed by the partitioning agent in the copolymer powder.

A heterocyclic methacrylate polymer system, developed originally as a low shrinkage polymer system, has been investigated as a drug release polymer and as a biomaterial for encouraging bone or cartilage regeneration. The system is based on poly (ethyl methacrylate) polymer powder mixed with tetrahydrofurfuryl methacrylate monomer and polymerized at room temperature (PEM/THFM). Promising results have been obtained with this biomaterial, and hence its water uptake properties were investigated in detall, in order to throw some light on the release processes that are involved in vivo and in vitro. Water soluble large molecule analogues were incorporated into the system; these additives increased the water uptake of the system. Isobornyl methacrylate was used as a diluent for the monomer to further reduce the water uptake of the system. In all cases the uptake kinetics did not obey simple diffusion theory, the process being very prolonged and complex.