Enzymatic Synthesis Of Phenolic Oligomers In Aquatic System And Investigations On Their Antioxidant Properties

Though polypropylene(PP)is one of the most widely used commodity polymers due to excellent properties,it is easy to suffer from uncontrolled oxidation during processing and application periods.Adding antioxidants,hindered phenols for example,is an effective way to reduce the potential oxidative degradation of PP.It is reported that hindered phenols with low molecular weight could easily departed from PP by migration and evaporation.There are various approaches to minimize the physical loss of phenolic antioxidants,among which increasing the molecular weight is an effective method.Enzymatic syntheses of polyphenols provide a new method to achieve hindered phenolic antioxidants with high molecular weight owing to mild reaction conditions and facile procedures.The innovation of this paper is that efficient syntheses of several phenolic oligomers use water as a medium,and these oligomers have better thermal stability and antioxidant properties.p-Cresol oligomer,which contain hindered phenol structure,was synthesized by enzymatic polymerization in SDS micellar system.The effects of the oligomers on the thermal stability of polypropylene were studied by thermal gravimetric analysis,differential scanning calorimetry analysis and the accelerated aging test.The results shows that the initial oxidation temperature of the p-cresol oligomer/polypropylene composite is increased by 32 ? as well as the oxidation induction time is increased by 27 min compared with that of pure polypropylene.p-Cresol oligomer/polypropylene composite has good long-term thermostable oxygen stability and the result of infrared spectroscopy analysis shows that there were not significant oxidative degradation of the polypropylene composite afteraging at 120 ? in air atmosphere for 156 h.Thermal decomposition kinetics analysised by Flynn-Wall-Ozawa method shows showed that the apparent activation energy of thermal decomposition of polypropylene is improved with addition of p-cresol oligomer.4-Methoxyphenol and 4-methylcatechol oligomers were prepared by enzymatic polymerization in aquatic system.Mass spectrometry analysis shows that the main components of the 4-methoxyphenol oligomer were hexamers,heptamers and octamer,while 4-methylcatechol oligomers were trimeric and tetramer.The structure of the phenolic oligomers chains were composed of phenylene and oxyphenylene units.4-Methoxyphenol oligomers have a good ability to scavenge DPPH and ABTS free radicals.The addition of these two phenolic oligomers as additives to the polypropylene material both can significantly improve the initial oxidation temperature and oxidation induction time of polypropylene,and the effect was better than the commercial antioxidants BHT and 1076.4-methoxyphenol oligomer/polypropylene showed good oxidation resistance,and the tensile strength did not decrease significantly after aging at 120 ? in air atmosphere for 600 h.