In photopolymer-based composites systems, light attenuation due to absorption and scattering from fillers induce variation in the light available throughout a composite. This typically leads to ‘top-down’ curing, creating stress concentration gradients within the composite and at substrate interfaces. This study examines the reaction kinetics of dimethacrylate-based filled materials using a unique visible-light free-radical photoinitator in an effort to create more uniform cure in thick specimens. Initiation with either a single component titanocene photoinitiator [bis(cyclopentadienyl)bis[2,6-difluoro-3-(1-pyrryl)phenyl]titanium (Irgacure 784, 1 wt%) or camphorquinone/ethyl 4-dimethylaminobenzoate (CQ/EDMAB, 0.2/0.6 wt%, respectively) was compared in triethylene glycol dimethacrylate (TEGDMA) and BisGMA/TEGDMA (70/30 wt%) resins. Silane-treated barium glass (0.4 µm) was used at various loading levels. Measurements included resin viscosity (viscometer) and reaction kinetics (FT-IR). Introduction of the titanocene initiator resulted in dramatically different kinetic profiles depending on the resin viscosity. At 10 mW/cm2 in BisGMA/TEGDMA resin (viscosity = 1.6 Pa*s), conversion of 64.4(±0.3)% was achieved, compared to 61.5(±0.2)% for the CQ/EDMAB control. At the same intensity, TEGDMA (viscosity = 0.05 Pa*s) reached a conversion of only 3.9(±0.4)%, compared to 72.8(±0.3)% for the CQ/EDMAB control. Incorporation of inorganic particulate filler into TEGDMA from 50-80 wt% resulted in minimal conversion at 50-60 wt% levels and moderate to high levels of conversion obtained at the more viscous 70-80 wt% filler levels. With the appreciable increase in performance at intermediate light intensities, which may indicate a critical interaction between excited state and ground state species, this initiating system has the potential to be used effectively in highly viscous materials with significant levels of organic or inorganic filler, where the light attenuation profile may offer a unique prospect for bottom-to-top rather than top-down photocuring.

Visible-light initiator with potential for bottom-up photocuring

249th National Meeting (2015)

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