AbstractThe enthalpies of combustion of poly(oxy‐1,4‐cyclohexylene) formed from 7‐oxabicyclo[2.2.1]heptane (1) and of its derivatives formed fromexo‐ andendo‐3‐methyl‐7‐oxabicyclo[2.2.1]heptane (2aand2b) have been measured. From literature values for the enthalpies of combustion of the liquid monomers, the enthalpies of polymerisation have been derived: −ΔH 0p(1→c)=44,3±1,9, 49,7±2,6, and 45.4±3,1 kJ mol−1, respectively. The results indicate a minimum strain energy in these polymers of ca. 15 kJ mol−1. The estimated entropies of polymerisation yield ceiling temperatures of 320, 240, 200°C respectively for the three bicyclic ethers.—The reasons for the discrepancy between our present −ΔH 0p(1→c) for theendocompound and t