Photo-induced Cross-linking Copolymerization Occurring With and Without Phase Separation

The photocurable compositions are based on the mixtures of components of various physical
properties and chemical structures. The structure of the network formed during the curing is
determined by the reactivity of the monomeric units and by the mutual solubility of the monomers and oligomers used. Bis-GMA 4-(2-hydroxymethacryloxypropoxy)phenyl]prOpane) is often used as a base material in dental resins. Due to its very high viscosity it is usually diluted with monomers of low viscosity; the most popular one being triethylene glycol dimethacrylate (TEGDM). In addition to external factors, the photopolymerization rates of such compositions depend on the monomer ratios in the feed. The optimum feed composition yields the highest value of the maximum polymerization rate 1-4]. However, good copolymer properties can be obtained when the monomers are miscible and the polymer network formed during the polymerization of multifunctional monomers is compatible with the monomers. In the case of limited solubility the increasing molecular weight of the polymer as the polymerization proceeds, causes that the mixture passes through a miscibility gap and a phase separation among components appears. Moreover, if corresponding polymers are not compatible, discrete segments of networks of different compositions will form. These effects should be observed
by naked eye as opacity of the product and reflected by kinetic curves.