Relative reactivities of cyclic ethers in cationic copolymerizations: Effects of ring strain and basicity

The relative reactivities of α‐monosubstituted cyclic ethers having rings of three to six members toward a cation were estimated from their copolymerizations with 3,3‐bis‐(chloromethyl)oxetane (M1) catalyzed by boron trifluoride etherate in methylene chloride at 0°C. It was found that the reactivity of these cyclic ethers was dominated by both the ring strain and the basicity. The following empirical equation was derived to represent the relative reactivity of cyclic ethers: log (1/r1) = −0.086ΔRS − 0.31ΔB + 0.57, where ΔRS and ΔB are constants, characteristic of ring strain and basicity of the cyclic ethers and determined from the differences in free energy of polymerization of the corresponding cycloalkanes and in basicity between M1 and M2 monomers, respectively. A good linear correlation was observed between the reactivities calculated from this equation and those obtained from the experiments.