Certain monovinyl (meth)acrylate monomers with secondary functionalities such as urethanes have been shown to exhibit extremely rapid curing rates. In this work, the polymerization mechanism, polymerization rate scaling, and relative oxygen inhibition are evaluated for an ultra-rapid butyl urethane acrylate and an analogous aliphatic urethane diacrylate. The aliphatic urethane diacrylate was found to have increased polymerization rates at higher initiation rates relative to the butyl urethane acrylate, primarily due to different termination mechanisms. Additionally, due to higher viscosity and crosslinking density, the aliphatic urethane diacrylate was found to exhibit a greater resistance to oxygen inhibition. The flux of oxygen into the aliphatic urethane diacrylate was 1/3 that of butyl urethane acrylate. Suppressed termination likely contributes to the rapid polymerization kinetics of butyl urethane acrylate. (C) 2008 Elsevier Ltd. All rights reserved.