Enzymatic Polymerizations Of Phenol Compounds And Investigations On Their Application Properties

Enzymes used as catalyst in organic synthesis were investigated extensively; however, there arerelatively less reports on polymerization catalyzed by enzyme. Polymerizations of phenol compounds canbe performed by using peroxidase as catalyst. The finding has attracted many scholars’ attention because itprovides a new method for producing phenol polymers under mild conditions without formaldehyde.In this paper, polymerization of phenol catalyzed by horseradish peroxidase was performed smoothly inaqueous micelle system. Due to no organic solvent added, the high catalytic activity of horseradishperoxidase is maintained. Tiny amount of enzyme is used but the reaction rate is very fast in aqueousmicelle system. The novel reaction system holds advantages of high efficiency, low cost and environmentalbenign. As a result, the practical performance of the enzymatic phenol polymerization will be enhancedgreatly. The yield of the phenol polymer increases by increasing the amount of surfactant from0.1to0.4g,and the final yield is up to95%. The phenol polymerization catalyzed by horseradish peroxidase in aqueousmicelle system can be performed effectively over a wide pH range from4to10and shows good acid-alkalitolerance. Phenol polymer obtained in aqueous micelle system often exhibits poor solubility. Interestingly,phenol polymer shows good solubility in acetone, THF, DMSO and DMF can be prepared inphosphate-citric acid buffer (pH=8) because of the salt effect on micelle. The yield of the phenol polymerobtained in the buffer increases from54.5%to80.6%when the dosage of sodium dodecyl benzenesulfonate rises from0.3g to0.5g. Meanwhile, the weight-average molecular weight of the polymerincreases from3.5×10~4to8.0×10~4. When the reaction temperature rises from20℃to50℃, the averagemolecular weight of the polymer increases but the yield increases first, and then decreases. The decomposition temperature of the soluble phenol polymer is higher than300℃and shows good thermalstability. A novel supported palladium complex catalyst is synthesized by using the obtained phenolpolymer as carrier. Heck reactions of aryl iodides, aryl bromides or activated aryl chlorides can becatalyzed by the complex smoothly and the yields of the product are higher than80%. The complex can bereused for Heck reaction of iodobenzene with styrene and yield of90.8%is obtained at the cycle of five.Enzymatic polymerization of p-cresol can also be performed smoothly in aqueous micelle system and theyield of the product is higher than90%. The average degree of the product is less than10probably due tothe phenol structure at the end of the molecular chain turns into quinine structure. p-Cresol oligomerdecomposes at200℃because of the low molecular weight and the presence of methyl. The structure of thep-cresol oligomer is very similar to the natural polyphenolic compounds, and also shows good free radicalscavenging activities. The concentration in mg/L that p-cresol oligomer inhibits free radical by50%(Ic50)was calculated and the result is33.3mg/L (for DPPH free radical) and3.4mg/L (for ABTS cation freeradical) respectively. The free radical scavenging activity is comparable with natural compound (rutin orpinoresinol) showing good performance. The synthetic method of p-cresol oligomer is very simple. Inaddition, it shows good stability in air and has no stimulating smell. As a result, p-cresol oligomer has goodapplication prospect as a novel antioxidant.p-Chlorophenol polymer and p-bromophenol polymer with moderate yields are synthesized in themixture of organic solvent and phosphate buffer (pH=7) by using horseradish peroxidase as catalyst. Thetype of the organic solvent has little effect on the polymer yield; nevertheless, the molecular weight of thepolymer varies greatly. p-Chlorophenol polymer and p-bromophenol polymer with weight-averagemolecular weight less than2.0×10~4are produced by choosing methanol as organic solvent. The volumeratio of organic solvent to buffer has great effect on the yield and molecular weight of the polymer. Ic50of p-chlorophenol polymer for DPPH free radical and ABTS cation free radical is240mg/L and11.1mg/Lrespectively. Under the same reaction conditions, Ic50of p-bromophenol polymer for DPPH free radical andABTS cation free radical is365mg/L and23.5mg/L respectively. It is obvious that the free radicalscavenging activity of p-bromophenol polymer is poorer than p-chlorophenol polymer. The reason isprobably due to the steric effect related to the larger bromine atom preventing the interaction of polymerchain with free radicals.