Oxidation-reduction polymers

Abstract

This review summarizes our work on the synthesis and redox properties of polymcrs with various quinone -hydroquinone systems. Information is given on our attempts to increase the chemical stability of the redox resins by suitable substitution and by other methods.The redox properties wcre thoroughly invcstigated (e.g. redox potentials, redox capadty, rate of thc redox reaction). A thcoretical treatmcnt is given for the redox behaviour of tetra-and hexa-valent redox systems.Redox resins can be used as insoluble, regenerable oxidants or reductants. By means of these resins some organic substrates could be dehydrogenated and several metal ions could be reduced or deposited .For several years we have synthesized polymer redox systems and have investigatcd their electrochemical properties. Polymer redox systems are known by the names oxidation-reduction polymers, redox polymers, redox resins and electron-transfer polymers. Water~swellable polymers which can reversibly be oxidized or reduced are usually named redox resins. The redox components of these polymers can be links of the polymer chains or they can be substituents of the chains. The chemical structure of the redox systems can be varied widely. There exist several reviews 1 -3 on this su bject: those of Cassidy can be especially recommended. This paper is a selective review of investigations of redox resins containing hydroquinone-quinone redox systems which have becn performed in our laboratories. SYNTHESlS OF REDOX RESINSRedox polymers may be addition polymers synthesized by polymerizing hydroquinone-quinone derivates which contain vinyl groups, or condensation polymers prepared by polycondensation of suitable compounds. They can also be prepared by polymer analogous reactions on preformed polymers.Examples of addition polymers are the redox resins which were investigated by Cassidy and bis co~workers 4 . They were prepared on the basis of vinylhydroquinone. As the hydroquinone·· quinone system inhibits poly~ merization, protecting groups (e.g. ether, acetate, benzoate) are usually introduced, which can be quantitatively removed after polymerization. A 181 Brought to you by | California Institute of Technol Authenticated Download Date | 8/11/15 2:01 PM

On Some New Oxidation—Reduction Polymers

“…The relatively large pore size should allow the quick inward diffusion of solvent. (5) The chemical stability of these special redox reagents is limited by the stability of the polysiloxane backbone, the stability of the Si-C-bonds involved with the redox moieties, and naturally by the stability of the quinoid systems themselves.…”