We have characterized the effective rate constants for termination/trapping (k(t/t)) and propagation (k(p)) for solvent-free cationic photopolymerizations of phenyl glycidyl ether for conversions up to 50%. We have performed dark-cure experiments in which active centers are produced photochemically for a specified period of time until the initiating light is shuttered off, and then the polymerization rate is monitored in the dark. This method is especially well suited for characterizing cationic polymerizations because of the long active center lifetimes. Our analysis provides profiles of the instantaneous kinetic rate constants as functions of conversion (or time). For photopolymerizations of phenyl glycidyl ether initiated with iodonium photoinitiators, k(t/t) and k(P) remain essentially invariant for conversions up to 50%. For the photoinitiator (tolycumyl) iodonium tetrakis (pentafluorophenyl) borate (IPB), the values of k(t/t) at 50 and 60 degreesC are 0.027 and 0.033 min(-1), respectively. The corresponding values of k(t/t) for diaryliodonium hexafluoroantimonate (IHA) are 0.041 and 0.068 min(-1). The values of k(p) at 50 degreesC for IPB and IHA are 0.6 and 0.4 L mol(-1) s(-1), respectively. (C) 2003 Wiley Periodicals, Inc.