AbstractCyclopolymerizations ofN‐allylmethacrylamide(1a)andN‐allylacrylamide(1b)are conducted over the temperature range below and above the ceiling temperature (Tc) ofN‐propylmethacrylamide(2a),one of the monofunctional counterparts of1a. Increasing the polymerization temperature extensively enhances the cyclopolymerizability of1aat temperatures in the vicinity of theTcof2a,while the cyclopolymerizability of1bincreases slightly with temperature. The polymerization tendency ofN‐propylacrylamide(2b),one of the monofunctional counterparts of1b,is lying high above the temperature range investigated and both monoallyl counterparts of1aand1bshowed similar polymerizabilities. The differences between the cyclopolymerizabilities of1aand1bare interpreted by applying the hypothesis that the lower the polymerizability of the corresponding monofunctional counterparts of the unconjugated dienes, the higher their cyclopolymerizabilities. Another point focused on the reversibility of intramolecular cyclization, because polymerization of1awas carried out in the vicinity of theTcof2a. It appears that the cyclic structure of poly(1a)consists exclusively of a 5‐membered ring whereas poly(1b)contains 5‐ and 6‐membered rings. The polymerization temperature does not affect the proportion of these two cyclic structures for both polymers. These results suggest that reversibility of intramolecular cyclization need not be taken into consideration to explain the cyclopolymerization behav