Cationic polymerization involving covalent propagating species

Cationic polymerizations of some cyclic imino ethers using methyl iodide as initiator were found to propagate via covalent growing species of alkyl iodide nature. The propagation mechanism of the polymerization was examined by direct observation of the reaction system by means of NMR spectroscopy and by indirect kinetic analysis. Among six monomers, 2‐oxazoline (1), 2‐phenyl‐2‐oxazoline (2), and 2‐phenyl‐5,6‐dihydro‐4H‐1,3‐oxazine (3) were found to be polymerized with CH3I via covalent growing species. On the other hand, 2‐methyl‐2‐oxazoline (4) and 5,6‐dihydro‐4H‐1,3‐oxazine (5) were polymerized with CH3I via ionic growing species. For the polymerization of 5‐methyl‐2‐oxazoline (6) initiated by CH3I, a mechanism of propagation via an equilibrium mixture of ionic and covalent propagating species (22 and 21, respectively) was presented. In all cases of the polymerizations of these six monomers by methyl p‐toluenesulfonate as initiator, the growing species were ionic ones having structures of the corresponding cyclic onium p‐toluenesulfonates.