Six methacrylate monomers have been synthesized for use as reactive diluents in dental composites and evaluated to investigate the relationship between molecular structure and monomer reactivity. Four were synthesized by reactions of glycidyl methacrylate (GMA) with various acids, 2-(2-methoxyethoxy)acetic acid (1), 2-(2-(2-methoxyethoxy)ethoxy)acetic acid (2), cyanoacetic acid (3), and benzoic acid (4); others were synthesized by reactions of GMA with diethyl hydrogen phosphate (5) or methanol (6). Monomers 1 and 2 are novel, 3 seems to be novel, 4 and 6 were synthesized via a novel method, and the synthesis of 5 was described in the literature. The monomers showed high crosslinking tendencies during thermal bulk polymerizations. The photo-, homo-, and copolymerization behavior of the monomers with 2,2-bis[4-(2-hydroxy-3-methacryloyloxy)phenyl]propane (Bis-GMA) were investigated. The maximum rate of polymerizations of monomers 2-6 was found to be greater than triethyleneglycol dimethacrylate, Bis-GMA, 2-hydroxyethyl methacrylate, and glycerol dimethacrylate. For the more reactive monomers (2, 3, and 4), the oxygen sensitivity of polymerization was found to be low due to a hydrogen abstraction/chain transfer reaction. The computationally calculated dipole moment and lowest unoccupied molecular orbital energies indicated that there seems to be a correlation between these quantities and reactivity for ester linked monomers (1-5), which was also supported by C-13 NMR data. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3787-3796, 2010