Radical cyclopolymerization of allyl methacrylate (AMA) was investigated in detail, especially under the specified conditions; that is, above the ceiling temperature for a head‐to‐tail propagation (ΔGht ≥ 0) in the polymerization of methacrylate. Thus the structure of the polymer obtained was examined by 1H‐ and 13C‐NMR and infrared (IR) spectroscopy; no existence of unreacted pendant methacrylyl groups was observed, which suggests that, as a cyclopolymerization mechanism of AMA, intermolecular propagation of growing radicals, followed by intramolecular cyclization or intermolecular propagation of the resulting uncyclized methacrylyl radical, occurs exclusively with methacrylyl group. Temperature dependency of cyclization constant Kc was unusual; Kc increased rapidly at elevated temperatures and no linear relationship of ln Kc vs. 1/T was observed. Five‐membered ring formation was favored at an elevated temperature and diluted monomer concentration. These results are discussed thermodynamically in terms of controlled ring closure in cyclopolymerization.

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