Acrylate-Terminated Macromonomers by Michael Addition

Abstract

A series of diacrylate macromonomers bearing alkoxysilyl units was prepared by convenient Michael addition of aminopropyl methyl diethoxysilane to 1,2-ethylene glycol diacrylate (EGDA), p-phenylene diacrylate (PDA) and 1,4-cyclohexanediol diacrylate (CHDA). The resulting macromonomers have been characterized in detail by NMR spectroscopy, vapor pressure osmometry (VPO) measurements and fast-atom bombardment mass spectroscopy (FAB-MS). Average molecular weights M̄n ranged between 530 and 1 300 g·mol–1 (VPO). FAB-MS and size exclusion chromatography (SEC) showed the formation of a homologous macromonomer series. Viscosities of the liquid monomers are relatively low, ranging from 0.082 to 8.30 Pa·s. This renders these compounds interesting as reactive diluents in dental composite formulations. Upon polymerization of the macromonomers, low volumetric shrinkage occurred, which was in the range of ΔV = 2.4 and 3.9 vol.-% at high conversion. Crosslinking was monitored by photo-differential scanning calorimetry (photo-DSC). Furthermore, composites were prepared by mixing 2,2-bis-[p-(2-hydroxy-3-methacryloxypropoxy)-phenyl]propane (Bis-GMA) with the new macromonomers, initiator and glass filler. The composites showed compressive strengths up to 244 MPa, flexural strengths from 22 to 42 MPa and Young's moduli between 870 and 3 070 MPa. The composite materials exhibited low volume shrinkage of about 2 vol.-% in comparison to over 3 vol.-% shrinkage of commercially available composites.