Photocationic polymerization for three cyclic acetals, namely 1,3-dioxolane, 1,3dioxepane and 1,3,6-trioxocane, respectively, has been studied. Several cationic photo-initiators (diaryliodonium or triarylsulfonium salts, and one arene-metal complex) have been used. Differential scanning photo-calorimetry (DPC) has been employed to record the dependence conversion versus time. DPC thermogrames, in turn, have been utilized to calculate the propagation reaction constants as well as the corresponding activation energies. The values for the propagation constants at 30degreesC are 1.6(.)10(2) L/mol(.)s for 1,3-dioxolane, using a diaryliodonium salt as photoinitiator, 1.6(.)10(3) L/mol(.)s for 1,3-dioxepane and 6.1(.)10(3) L/mol(.)s for 1,3,6-trioxocane, respectively, in the presence of a triarylsulfonium salt as photoinitiator. The activation energies are in the range of 9.6divided by19.6 kcal/mole.