Photoreactivity of expanding monomers and epoxy-based matrix resin systems

The relative photoreactivity of five expanding monomers (EMs) in homopolyme rization, and as comonomers in a candidate low shrinkage dental matrix resi n, were evaluated. The EMs were 2,8-dimethyl-1,5,7,11-tetraoxaspiro[5.5]und ecane (DM-TOSU); 3,9-diethyl-3,9-dipropionyloxymethyl-1,5,7,11-tetraoxaspir o[5.5]undecane (DEDPM-TOSU); 1,3-dioxane-2-one (DOO); 4-methyl-1,3-dioxane- 2-one (M-DOO); and 5,5-diethyl-1,3-dioxane-2-thione (DE-DOT). The candidate low shrinkage resin system was an 80/20 mixture of UVR-6105 epoxide/polyte trahydrofuran (M-n approximate to 250). All reaction mixtures contained a d iaryliodonium salt as a photoinitiator and camphorquinone as photosensitize r. Reactivities were evaluated using photodifferential scanning calorimetry . For homopolymerizations, the reactivity ranking (based on time to exother m peak and total enthalpy) was DE-DOT much greater than DM-TOSU > DOO > M-D OO greater than or equal to DEDPM-TOSU. In the comonomer system, the reacti vity ranking was M-DOO > DEDPM-TOSU > DM-TOSU > DOO greater than or equal t o DE-DOT. This experimental work was substantiated and extended by molecula r modeling studies employing the AM1 semiempirical method. Heats of formati on of protonated EM structures, and heats of formation and potential. energ ies of possible polymerization pathways were estimated. The relative reacti vities of EM-based polymerization systems are related to chemical structure and the dominance of the most favored reaction mechanism. (C) 2000 John Wi ley & Sons, Inc.