The role of cationic and covalent active centers in the polymerization of 2-methyl-2-oxazoline initiated with benzyl bromide

It was shown that in the polymerization of 2-methyl-2-oxazoline initiated with benzyl bromide in nitrobenzene the equilibrium constant of the interconversion of cationic and covalent active centers could be measured over a wide range of temperatures, thus making the thermodynamic parameters of this reaction available. The "temperature jump" method was used to measure the rate constants and the activation parameters of the reversible transformation of the ionic active centers into covalent ones. The apparent rate constant of the chain growth in this polymerization was measured, and individual rate constants of chain growth on ionic and covalent centers were approximated using systems in which one kind of active centers strongly prevails. The obtained data allowed for a complete description of the individual reactions and for an estimation of the contribution of these reactions to chain growth. Because of the higher reactivity of the ionic species and higher rate of ionization without monomer participation (thus, through intramolecular ionization), there are no conditions at which the covalent species may prevail in the chain growth. Even if there is a large excess of covalent species, propagation proceeds on the ionic ones. The effective monomer concentration is approximately 10(3) mol/L, indicating that at 1 mol/L of monomer the internal ionization proceeds 10(3) times faster than the external ionization (with monomer).