Lewis acid-surfactant complex catalyzed polymerization in aqueous dispersed media: cationic or radical polymerization?

Abstract

Cationic polymerization is a useful polymerization technique in the production of a number of commercial polymers but is notoriously challenging to perform due to side-reactions with atmospheric water. Despite this, with the development of new water tolerant Lewis acid surfactant complexes, it has been reported that cationic polymerization of vinylic monomers can be readily conducted in aqueous dispersed media achieving molecular weights in excess of 100 kg mol⁻¹. Here, evidence is provided that suggests these reactions do not occur via a cationic pathway. On the basis of the extremely high molecular weights obtained, the oxygen sensitivity of the reaction, the inhibition of the reaction by radical inhibitors, evidence of radical transfer events by mass spectrometry, the ability to (co)polymerize monomers not capable of undergoing cationic polymerization, and the detection of radical species by using spin trapping experiments combined with electron spin resonance (ESR) spectroscopy, it is suggested that a radical polymerization is occurring in these reactions. The implications this may have for potential use of cationic polymerization in the synthesis of high molecular weight polymers in aqueous media is highlighted.