Photo-differential scanning calorimetry experiments were used to determine effective kinetic constants for propagation and termination for a series of unsteady-state divinyl ether polymerizations at different temperatures and light intensities. For these cationic photopolymerizations the reaction rate and limiting conversion were both found to increase as the reaction temperature was increased. At all temperatures exhibited a dramatic increase at the start of the reaction, the profile for the propagation rate constant k(p) plateaued at a value between 5 and 301 mol(-1)s(-1) (depending upon temperature) and then decreased as the reaction reached a limiting conversion owing to trapping of the active centres. The effective termination rate constant k(t) was very low, with active centre lifetimes approaching 20 min. The overall activation energy for polymerization was found to be 26.5 +/- 3.2 kJ mol(-1).