Photopolymerization kinetics and viscosity behavior of five different two-monomer systems forming hydrogen bonds and composed of mixtures of a high viscosity monomer (HVM) and a low viscosity monomer (LVM) at various molar ratios were investigated at six polymerization temperatures. The monomers used were mono- or dimethacrylates. Detailed viscosity measurements of the monomer mixtures showed significant negative deviations from the theoretical values (characterized by excess logarithm viscosities) indicating that interactions between the molecules of the same type (in individual monomers) are stronger than those between two molecules of different types (HVM and LVM). The photopolymerization kinetics were analyzed from the point of view of the appearance, viscosity and temperature behavior of the most reactive composition (MRC), the one showing the highest Value of the maximum polymerization rate within a range of the HVM: LVM ratios. It was found that MRC appearance is determined mainly by the initial viscosity of the two-monomer system, whereas the functionality of the monomers (and network formation) is much less important (MRC is observed even in linear systems). The initial viscosity of all the monomer mixtures showing MRC lay in the range of 0.06-2 Pa s, which is narrow compared to the range of viscosities of the monomers (approximately 10(-3)-10(3) Pa s). (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116:280-287, 2010