Synthesis and Polymerization of Epoxy Methacrylates, 2. Acylated Epoxy Methacrylates and their Copolymers

Abstract

Partially (20–75%) acylated isopropylidene-bis[1,4-phenyleneoxy(2-hydroxytrimethylene)] dimethacrylate (BisGMA) was prepared by a single step reaction of 2,2-bis[4-(2,3-epoxypropoxy)phenyl]propane (DGEBA) with methacrylic acid (MAA), methacrylic anhydride (MAAn) and/or acetic anhydride catalyzed by 0.8 mol-% N-methylimidazole at 90–100°C. In any case, MAA was substituted by an equimolar quantity of the anhydride. The reaction kinetics of DGEBA with MAA and MAAn follows a first order law up to a conversion of epoxy groups corresponding to the initial molar ratio of MAAn. For different mole fractions xMAA, the reaction rate was found to be directly proportional to x0.5MAA. The viscosity of BisGMA decreased with an increase in the acylation degree. Acylated BisGMA was copolymerized with triethylene glycol dimethacrylate (TEGMA) by use of a redox initiator system at room temperature and with vinyltoluene (VT) initiated by di-tert-butyl peroxide at 150–200°C, respectively, both in the presence of 70–76 wt.-% of quartz filler. Different dependencies of the content of sol and the conversion of C=C double bonds were observed for thermally polymerized composites from VT with acetylated and methacrylated BisGMA, respectively. Methacrylated BisGMA yielded composites with reduced water uptake. The higher network density of the polymer matrix with methacrylated BisGMA resulted in a higher glass transition temperature Tg and a higher storage modulus of the composites. The initial temperature of weight loss of composites with VT was increased from 230°C for composites with BisGMA up to 258°C for composites with BisGMA methacrylated to a degree of 40%.