Influence of selected components on crosslink density in polymer structures

Bifunctional methacrylates polymerize to form crosslinked polymer structures which may be characterized by the quantity of remaining double bonds and by the crosslink density. This study investigated the influence of composition variation on the crosslink density of model methacrylate polymers. It was hypothesized that addition of a monofunctional monomer would reduce crosslink density and that compositions giving rise to many centers of polymer growth would result in increased crosslink density. Unfilled resins with varying content of BisGMA, TEGDMA, a monofunctional monomer, camphoroquinone, and amine were polymerized by visible light irradiation. After polymerization, the quantity of remaining double bonds and the Wallace hardness were determined. Polymer softening upon storage in ethanol was taken as a measure of the crosslink density. After ethanol storage, the relationship between hardness number and amount of monofunctional monomer showed a minimum. At same quantity of remaining double bonds, a high content of camphoroquinone compared to amine resulted in reduced softening in ethanol. Composition influenced not only remaining double bonds but also the crosslink density of the resulting polymer structures.