AbstractMethods have been developed for the determination of weight and number average molecular weights of copolymers of trioxane containing oxyethylene units by light scattering and osmotic pressure measurements, respectively. The ratio Mw/Mnfor a number of whole polymers is close to 2, in good agreement with the estimate of this ratio indirectly determined from the effect of chain transfer agent. Dilute solution and melt viscosity measurements have also been made. The melt viscosity at zero shear rate is approximately proportional to the 3.4 power of Mw, both for polymers as polymerized and for a blend of two such polymers. The dependence of melt viscosity on shear rate can be fitted to the BUECHE‐HARDINGemperical equation, but the values of MRcalculated from this equation are much smaller than Mw. For the blend MRis higher than that of either component. All of the results are in accord with those found for other polymers of about the same molecular weight distributio