KINETICS AND PROPERTIES OF A PHOTOPOLYMERIZED DIMETHACRYLATE OLIGOMER

The free radical photopolymerization of two urethane dimethacrylate oligomer systems, used in dentistry as elastomeric impression materials, was investigated. When cured in thick section, these materials have a limited depth of cure that depends on the irradiation conditions. A mathematical model is presented that considers the spatial dependence of the polymerization process on the attenuated radiation intensity and the local concentration of radical scavenging inhibitors. The predicted dependence of the depth of cure on the logarithm of radiation intensity and exposure time is confirmed. DSC studies revealed that for thin sections the rate of polymerization had the conventional square root dependence on radiation intensity over a 1000-fold range of intensities. These results are discussed in terms of a decoupling of the mobility of the pendant methacrylate group from the chain to which it is attached. In an oxygen environment, inhibition of the photopolymerization caused an induction period that was proportional to the reciprocal radiation intensity. Modulus measurements during cure also illustrated the rapid nature of photopolymerization process and showed that in comparison to conventional two-component materials used for the same purpose the rates of buildup in properties for the photocured materials were superior. The tear energy of the cured photocured materials were compared with conventional types of elastomeric impression material, and the differences were interpreted in terms of energy dissipation mechanisms.