Quasiliving Cationic Polymerization of Styrene and Isobutylene: Run Number and Apparent Rate Constant of Ionization by TiCl4 and Energies of Activation of Elementary Reactions

The quantity k(p)/k(-i) was measured from first-order kinetic data for cationic quasiliving polymerization of styrene and isobutylene initiated with 5-tert-butyl-1,3-bis(2-chloro-2-propyl)benzene (bDCC)/TiCl4 in 60/40 MCHex/MeCl, via analysis of an initiation event termed rapid monomer consumption (RMC). RMC is characterized by an initial period of high polymerization rate followed by slower first-order decay in monomer concentration and is due to a larger ionization rate for the initiator compared to the polymer chain end. The value of k(p)/k(-i) was used in conjunction with the apparent rate constant for propagation, k(app), to calculate apparent rate constants of chain-end ionization, k(i), for both monomers at -60, -70, -80, and -90 degrees C, independently of k(p). Rate constants of ion-pair collapse and ionization equilibrium were calculated assuming published values of kp. Apparent energies of activation for k(p)/k(-i) of -2.4 and -4.6 kcal/mol were determined for styrene and IB, respectively. Apparent energies of activation for ionization, propagation, and ionization equilibrium were calculated for both monomers. Rates of chain-end ionization and ion-pair collapse were both higher and more sensitive to temperature for polyisobutylene than polystyrene