Fast-reacting Novel Monomethacrylates

Novel monomethacrylates with high reaction rates when added to conventional dental composite resin formulations may favorably affect both overall reaction rate and a number of the physical properties. Objective: To investigate the possible mechanism behind the higher reaction rates of a group of these monomethacrylates a series of substituted and non-substituted phenyl carbamate ethyl methacrylates were synthesized and the reaction kinetics determined. Methods: The experimental phenyl carbamate methacrylates were synthesized in the lab and contain either para, meta or no aromatic ring substitution with a methoxy group. The other variation was the orientation of the carbamate with either the nitrogen or oxygen of the carbamate proximal to the phenyl group. The control monomer was HEMA. Since most of these monomers are solids at room temperature, melting points were determined (up to 103oC). Dichloromethane solutions of each monomer were made, DMPA photoinitiator was added at 0.1 wt% of the monomer and the solvent evaporated. Kinetics were determined with differential scanning calorimetry at 110oC, using a bifurcated light guide from a Novacure light with a 365 nm filter at 5 mW/cm2, and the maximum rates of polymerization (Rp max) compared. Results: The Rp max average of 4 specimens for each of the monomers relative to HEMA were as follows: PhNCOma, 2.2; 4-MeOPhNCOma, 2.4; 3-MeOPhNCOma, 1.5; PhOCNma, 1.7; 4-MeOPhOCNma, 1.6; and 3-MeOPhOCNma, 1.6. ANOVA determined that there were significant differences in Rp max such that PhNCO form > PhOCN > HEMA. The substitutions of the PhOCN did not significantly affect the Rp max. In the PhNCO form the para-methoxy > no substitution > meta-methoxy. Conclusions: There may be an electronic contribution to the mechanism of the faster reaction due to the electron donating capacity of the methoxy substitution especially when the nitrogen is proximal to the phenyl. Supported by NIH grant K08DE14085.