BIMODAL MOLECULAR-WEIGHT DISTRIBUTION IN CARBOCATIONIC SYSTEMS WITH FREE IONS AND ION-PAIRS OF EQUAL REACTIVITIES BUT DIFFERENT LIFETIMES

Monte Carlo calculations and numerical integrations are used to study molecular weight distribution (MWD) in carbocationic polymerization an d to illustrate the effect of equilibrium constants, rate constants, a nd concentration of common ions on MW and MWD. It is demonstrated that bimodal molecular weight distribution is obtained when exchange betwe en ions and ion pairs of similar reactivities is slow and their lifeti mes are sufficiently different. Bimodal MWD is converted to narrow (Po isson) distribution in the presence of salts with common ions; molecul ar weights in these systems grow linearly with conversion like in livi ng polymerization.