QUANTUM-CHEMICAL ESTIMATION OF THE ROLE O F COMPETITIVE REACTIONS IN CATIONIC POLYMERIZATION OF BUTADIENE

Competition of various reactions of model butadiene carbocations occur ring in the course of cationic polymerization was studied using the me thod of modified neglect of diatomic overlap (MNDO). It is shown that, out of all the possible reactions responsible for the partial loss of unsaturated bonds in polybutadiene, the most effective is the reactio n of cyclization of active centers in which participate the 1,2-units of growing chains. For secondary cyclic carbocations formed in this re action, chain propagation has the highest energy preference; at the sa me time, the isomerization of these cations into tertiary cations is p ossible. The latter tend to undergo deactivation via proton transfer t o the monomer; for tertiary cations, this reaction is more favorable t han chain propagation.