Copolymerizations of 3.3‐bis(chloromethyl)oxacyclobutane with β‐propiolactone and γ‐butyrolactone by lewis acids: “Two‐state“ polymerization mechanism

A “two‐state” polymerization mechanism is proposed to explain the previously reported abnormal sequence distributions in the copolymers from 3.3‐bis(chloromethyl)oxacyclobutane (BCMO) and β‐propiolactone (PL) prepared with SnCl4 or BF3OEt2 as catalyst. Long BCMO sequences are formed by the normal cationic mechanism, whereas formation of long PL sequences is explained by the “coordinated” cationic mechanism, which assumes the polymerization of PL molecules which are coordinated to the catalyst. The lactone monomers coordinate to the catalyst or to the propagating cation through the carbonyl oxygen atoms, and this is supposed to be an important factor for controlling the operation of the two mechanism. β‐butyrolactone (BL) is particularly strongly coordinated and so produces alternating copolymers with BCMO.