Cationic polymerization of cyclic amines, 5. Polymerization of N‐tert‐butylaziridine

The polymerization of N‐tert‐butylaziridine (TBA) in dichloromethane with different cationic initiators leads to quantitative conversion. With triethyloxonium tetrafluoroborate (TEFB), initiation is rapid and the molecular weights of the polymers increase with increasing [TBA]/[TEFB] ratios. In contrast with other polymerizations of N‐substituted aziridines, termination reactions are absent. This is ascribed to the high steric hindrance of the tert‐butyl group which makes a nucleophilic attack of a polymeric amino function on the growing species (aziridinium ion) impossible. Poly(TBA) obtained by precipitation from its solution shows a high degree of crystallinity as is shown by its mp of 142°C (DSC) and by its well resolved X‐ray diffraction diagram. The viscosities of aqueous solutions of the hydrochloride of poly(TBA) show typical polyelectrolyte behaviour.