Recent Trends in Polymer Supported Catalysts pp. 63-90
Authors: (G. Rajesh Krishnan, Krishnapillai Sreekumar, Department of Applied Chemistry, Cochin University of Science and Technology, Cochin, Kerala, India)
Abstract: A polymer supported catalyst is a reactive system in which the catalyst or more correctly the catalytic centre is attached to a polymeric molecule. The catalytic centre is either an inherent part of the polymer, which may be a part of the monomer and which will be added to the polymer during polymerization, or attached to a previously formed polymer by some kind of chemical (covalent bonds) or physical (encapsulation) methods. These two situations can be represented as shown in figure 1. The polymer species of these types of catalysts may be a linear or a crosslinked entity, and again the latter have proved particularly useful. Polymeric catalysts are generally used in catalytic quantities relative to reaction substrates, and can often be reused many times. The attachment of a catalyst to a support may improve its stability and selectivity. On the other hand, increased experimental convenience arising with a polymeric catalyst may be offset by a significant reduction in reactivity associated, for example, with diffusional limitations imposed by resin supports. Recent interest in the development of environmentally benign synthesis has evoked a renewed interest in developing polymer-bound catalysts and reagents for organic synthesis that maintain high activity and selectivity. [1, 2] A wide variety of catalysts have been supported in this way, ranging from strong acids and bases (ion-exchange resins), transition-metal complexes, organic catalysts and photosensitizers right through to the highly specific enzyme catalysts.