DESIGN AND DEVELOPMENT OF ISOCYANATOACRYLATES AS DENTAL ADHESIVES

During the last 12 years, significant progress has been made in the de velopment of dental adhesive systems. Some of the more promising syste ms are based on multifunctional structures that contain polymerizable vinyl double bonds and reactive isocyanate groups. The utility of comp ounds with such structures as adhesives arises in part because their i socyanate functionality is available for reaction independently, witho ut compromising the reactivity of the vinyl groups. The hypotheses tes ted in this investigation were: (1) that the monomer reactivity ratios (r(1), r(2)) for the free-radical-initiated copolymerization of ethyl alpha-isocyanatoacrylate (alpha-EIA) and 2-isocyanatoethyl methacryla te (IEM) with selected vinyl monomers can be determined; (2) that thes e reactivity ratios can be used to establish Q (reactivity) and e (pol arity) values for alpha-EIA and IEM; and (3) that these reactivity par ameters can be useful in designing copolymers with controlled composit ions for dental adhesive applications. The free-radical copolymerizati on characteristics of alpha-EIA and IEM were studied. The isocyanate m onomers were copolymerized at seven comonomer ratios with n-butyl acry late (NEA), methyl methacrylate (MMA), and styrene (STY). Reactivity r atios, r(1) and r(2), were calculated for each of the copolymer system s, giving: IEM (r(1)) = 0.38 and STY (r(2)) = 0.44; IEM (r(1)) = 1.19 and MMA (r(2)) = 0.84; IEM (r(1)) = 2.50 and NBA (r(2)) = 0.40; alpha- EIA (r(1)) = 2.20 and STY (r(2)) = 0.06; alpha-EIA (r(1)) = 7.00 and M MA (r(2)) = 0.10; and alpha-EIA (r(1)) = 23.50 and NBA (r(2)) = 0.04. The Q (reactivity) and e (polarity) values for IEM and alpha-EIA were calculated from r(1) and r(2) with use of the Alfrey-Price equations, giving, for IEM, Q = 0.89 and e = 0.60, and, for alpha-EIA, Q = 7.64 a nd e = 0.74. These reactivity parameters are useful for tailoring copo lymers with controlled compositions and properties. Based on these cal culated reactivity parameters, several copolymers of IEM [for example, IEM/2-hydroxyethyl methacrylate (HEMA)] are currently being prepared and evaluated as adhesives.