Kinetic Study on the Capping Reaction of Living Polyisobutylene with 1,1-Diphenylethylene. 1. Effect of Temperature and Comparison to the Model Compound 2-Chloro-2,4,4-trimethylpentane

The addition reaction of 1,1-diphenylethylene to polymeric and dimeric isobutylene living chain ends in the presence of TiCl 4 was investigated in hexane/MeCl 60/40 (v/v) at −80 to −40 °C using on-line UV−vis spectroscopy. The apparent equilibrium constants of capping/decapping, K e, and the apparent rate constants of capping, k c K i, were directly measured, and from these values, the corresponding rate constants of decapping, k d, were calculated. The activation energy is found to be apparently negative for the capping reaction ( k c K i ) and positive for the decapping reaction ( k d ). However, the respective activation parameters for the polyisobutylene differ significantly from those of the dimer; i.e., the chain length affects the kinetics of the capping/decapping reaction.