Bismethacrylate-based hybrid monomers via Michael-addition reactions

Bismethacrylate monomers and macromonomers bearing various alkoxysilyl unit s were prepared by convenient Michael addition of ethylene glycol acrylate methacrylate (EGAMA) and ethylene glycol bisacrylate (EGBA) to various alph a,omega -alkoxysilylamines. The resulting monomers and macromonomers have b een characterized in detail by NMR spectroscopy, VPO measurements and FAB-M S. Average molecular weights M-n ranged between 530 and 1600 (VPO) in addit ion reactions with bisacrylates. FAB-MS evidenced the formation of a homolo gous macromonomer series. Viscosities of the liquid monomers are relatively low, ranging from 52 to 305 mPa.s. This renders these compounds interestin g as reactive diluents in dental composite formulations. Polymerization of the monomers and macromonomers resulted in low volumetric shrinkage in the range of DeltaV = 2.2-7.8% at high methacrylate conversion. Crosslinking wa s monitored by photo-DSC. Furthermore, composites were prepared by mixing B is-GMA with the new hybrid monomers, initiator and glass filler. The compos ites showed compressive strengths of 190-329 MPa, flexural strengths from 2 3 to 53 MPa and Young's moduli between 2090 and 5060 Mpa. Low volumetric sh rinkage was observed also for the composites upon photopolymerization, rang ing from only 0.8% to 2.2% in comparison to over 3% shrinkage of commercial ly available composites. Besides the viscosity reducing effect due to the b ranched structure, the pendant alkoxysilyl groups of the synthesized hybrid monomers can be polymerized to form nanoparticles with reactive acrylate s urface, permitting the in situ preparation of nanocomposites.