UNIFIED APPROACH TO LIVING AND NONLIVING CATIONIC POLYMERIZATION OF ALKENES

The observation of various features of living polymerizations ('theoretical' molecular weights, narrow molecular weight distribution) in a large number of carbocationic polymerizations has led to the conclusion that termination and transfer were suppressed in these 'living' systems, while they played a predominant role in the 'classic' carbocationic polymerizations. This suppression has been attributed to the presence of new types of active sites, such as 'stretched' covalent bonds or 'stabilized' carbocations. In the present article, a comparison of the data observed with the 'classic' and the 'living' systems shows that the active sites are similar, with only a change in the relative proportion of carbocationic species, which reduces the rate and favors complete initiation. This means that these 'living' systems are generally only apparently living, since termination and transfer reactions also occur and are hidden because the molecular weights of the 'living' polymers are typically low. Transfer and termination may, however, be considerably reduced or even suppressed by working at very low temperatures, as is also the case for 'classic' systems.