Abstract

Cationic initiation in general and the cation donor (initiator)/Friedel-Crafts acid (coinitiator) initiating system in particular are reviewed. The efficiency of a particular initiating system depends on the reactivity of the initiating cation relative to that of the propagating center. The strength of the Friedel-Crafts acid and the nucleophilicity of the formed counteranion also affect the rates of initiation and propagation as well as the influence of solvent polarity. Controlled initiation in the absence of chain transfer, the inifer technique, and living cationic polymerization systems are reviewed. These systems have resulted in head group control, molecular weight, and end group control, and in the synthesis of well-defined materials with controlled architecture, molecular weight, molecular weight distributions, and end functionalities.