AbstractThe cationic copolymerization of dioxolan (DOL) and tetroxan (TEX) at a mole‐ratio of 9/1 with BF3OEt2in toluene was studied by gas chromatography and NMR. The very reactive TEX was consumed at an early stage, whereas DOL was consumed slowly until an equilibrium conversion was reached. Correspondingly, the fraction of formal units in the copolymers decreased gradually with conversion. Therefore TEX is both kinetically and thermodynamically more reactive than DOL. As a by‐product, a significant amount of trioxepan was found, which indicates a rather facile back‐biting rea