The copolymerization of trioxane (TO) (100 mol %) with the diglycidyl ether of 1,4-dihydroxy-diphenyl-dimethyl-methane (DE-Ph) (5-25 mol %) catalysed by BF(3)OEt(2) in nitrobenzene was studied. The kinetics of the polymerization process was followed gravimetrically and dilatometrically in the temperature range of 30-60 degrees C. It was established that no homopolymers were formed. The copolymers obtained show high alkaline and thermal stability. The copolymerisation is inhibited at increased DE-Ph levels. The copolymers were characterised also by their infrared (IR) spectra and differential scanning calorimetry (DSC).