Synthesis of polymers containing pseudohalide groups by cationic polymerization 15. Study of the functionalizing living cationic polymerization of 2-methyl-2-oxazoline in the presence of trimethylsilylazide

The cationic polymerization of 2-methyl-2-oxazoline initiated by benzyl bromide (BzBr) in the presence of trimethylsilylazide (TMSA) has been investigated. FT-IR, 1H-NMR and size exclusion chromatography analyses of polymers showed that initiation took place on BzBr, and the azide functionality fN3 was high and even complete when the [TMSA]/[BzBr] ratio was sufficiently high. The plot of Mn versus yield of azided poly(N-acetylethylenimine) gave a straight line showing that the living characteristics of the polymerization system were preserved in the presence of TMSA, although a kinetic study showed a decrease of the polymerization rate. The azide terminated polymer did not propagate but constituted a dormant species. Discussion of the results allowed to conclude that the azidation process consisted in an exchange between the brominated active species and TMSA to form dormant azided chain ends, as shown by the polydispersity index of the azided polymer which was still low. It was also shown that the azidation process was only observed in the presence of monomer, which is explained by the assumption that the azidation consists in a nucleophilic attack of bromide anion coming from the active species solvated by the monomer, onto TMSA. A brief kinetic analysis allowed us to calculate the propagation rate constant in our conditions (80°C, acetonitrile) and the rate constant of azidation reaction.