Diaryliodonium salts undergo facile reduction by the dialkylborane, 9-BBN. The combination of these two reagents constitutes a redox couple that can be employed as a convenient and versatile initiator system for the cationic polyrnerizations of styrenic monomers, vinyl ethers and the ring-opening polymerizations of cyclic ethers and acetals including; epoxides, oxetanes, tetrahydrofuran, and 1,3,5-trioxane. The polymerizations of these monomers can be carried out in either neat monomer or under solution conditions. Typically, the redox cationic polymerizations of the above monomers are rapid and exothermic. Optical pyrometry (infrared thermography) was employed as a convenient method with which to monitor and optimize the aforementioned redox initiated cationic polymerizations. Studies of the effects of variations in the structure and concentrations of the diaryliodonium salt and 9-BBN on the polymerizations of various monomers were carried out. A mechanism for the redox cationic initiation of the polymerizations was proposed. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5639-5651, 2009