Enzyme-catalyzed condensation reactions for polymer modifications

The enzyme-catalyzed condensation is reviewed in view of its use in polymer modification reactions. The formation of esters and amides is most facile when (1) the reaction is carried out in a non-aqueous medium, and (2) the acyl donor contains a good leaving group. However, it is sometimes possible to relax these requirements. Thus, screening and selection of an appropriate enzyme and optimization of the reaction conditions can facilitate esterification and amidation reactions. Water or methanol can be physically removed through the use of vacuum or molecular sieves in order to shift the equilibrium to products and to enhance reaction yield,. For a propitious enzyme-polymer pair, the reaction can proceed even in water without a good leaving group. As illustrations, lipase-catalyzed syntheses are described for the amide of carboxymethylcellulose, substituted acrylic monomers, fatty acid esters of cationic guar, and fatty acid diesters of poly(ethylene glycol).