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 initia ted with benzyl bromide in nitrobenzene the equilibrium constant of th e interconversion of cationic and covalent active centers could be mea sured over a wide range of temperatures, thus making the thermodynamic parameters of this reaction available. The ''temperature jump'' metho d was used to measure the rate constants and the activation parameters of the reversible transformation of the ionic active centers into cov alent ones. The apparent rate constant of the chain growth in this pol ymerization was measured, and individual rate constants of chain growt h on ionic and covalent centers were approximated using systems in whi ch one kind of active centers strongly prevails. The obtained data all owed for a complete description of the individual reactions and for an estimation of the contribution of these reactions to chain growth. Be cause of the higher reactivity of the ionic species and higher rate of ionization without monomer participation (thus, through intramolecula r ionization), there are no conditions at which the covalent species m ay prevail in the chain growth. Even if there is a large excess of cov alent species, propagation proceeds on the ionic ones. The effective m onomer 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).