Salt and solvent effects in “living” carbocationic polymerization

Abstract

AbstractCarbocationic polymerization is strongly affected by medium and salt present in the system. The increase of solvent polarity enhances overall rates of cationic polymerization because it increases the proportion of carbocations in equilibrium with dormant covalent species. Higher solvent polarity might also increase molecular weights due to the reduction of transfer to counterions and may broaden polydispersity by slowing down an exchange between active and dormant species. Added salts may increase the proportion of ionic species by the ionic strength effect. The salts with common ions suppress free ions and lead to a monomodal molecular weight distribution by eliminating free ionic species with long lifetimes. The addition of tetrabutylammonium salts in the polymerization of styrene, initiated by 1‐phenylethyl chloride and catalyzed by tin tetrachloride is a typical example. The special salt effect based on exchange of counterions may enhance or reduce the proportion of ionic species and may accelerate the exchange between active and dormant species, affecting the polymerization rates and polydispersities.