Enzymatic Polymerization of Phenols Catalyzed by Chloroperoxidase in the Presence of Ionic Liquids/Quaternary Ammonium Salts

A green enzymatic approach for the synthesis of phenol polymersfrom substituted phenols monomer by chloroperoxidase(CPO)-catalyzed H2O2-oxidation was proposed in this paper. The yield and thermal stability of polymers of p-methyl phenol, p-ethyl phenol, p-propyl phenol, p-phenyl phenol and p-hydroxy-cinnamic acid were studied based on the presence of imidazolium-based ionic liquids (ILs) or quaternary ammonium salts (QAS), the effect of structure of the substrates and the reaction microenvironment. The results showed that the introduction of little amount of ILs/QAS can improve the production of polymerization of phenols efficiently, in which ILs/QAS with bigger cation group and shorter hydrophobic chain was much more effective, while the influence of ILs/QAS amount on polymerization of phenols showed a "ball type" pattern. Moreover, it was found that p-substituted phenol and electron-donating group were more beneficial to the increase of yield and thermal stability of phenol polymers compared to o-substituted phenol and electron-withdrawing group. However, the steric hindrance was increased with the increasing size of substituent group, which was not beneficial to the polymerization of phenols. The pH value should be controlled as weak acid or even near-neutral to avoid competitive side reaction, while the adding of H2O2 should be in a batch type to suppress the oxidative damage of heme caused by the instantaneous concentrated H2O2. The mechanism of polymerization was also analyzed and proposed based on the characteristics of structure of CPO active site.