Synthesis And Oxidative Stability Of Polyethylene Glycol Bridged Hindered Phenolic Polymeric Antioxidant

Polyethylene glycol with hydroxyl structure is a linear polymer with good thermal stability,and its terminal hydroxyl group can graft functional groups to synthesize functional compounds of polymer structure.Hindered phenolic antioxidants are widely used in the field of polyolefins because of their superior antioxidant properties and minimal impact on the appearance and color of polymer products.However,most of the current industrial antioxidants are small molecule compounds,which have the disadvantages of poor thermal stability,volatility,and migration resistance in practical applications.Polyethylene glycols with modified groups provide an idea to develop and synthesize new structures of high molecular weight antioxidants.By modifying the end hydroxyl groups of polyethylene glycols with antioxidant function,high molecular weight hindered phenolic polymeric antioxidants can be synthesized.In this thesis,three molecular weight polyethylene glycol bridged hindered phenolic polymeric antioxidants,namely PEG1500-phenol,PEG2000-phenol,and PEG4000-phenol,were synthesized by using a series of polyethylene glycols with different chain lengths as bridged groups andβ-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride as functionalized groups.The structures of the synthesized products were demonstrated by infrared spectroscopy(FT-IR),nuclear magnetic hydrogen spectroscopy(~1H-NMR),and ultraviolet-visible spectrophotometry(UV)to be consistent with the expected structures,and the hindered phenolic groups were successfully grafted on the polyethylene glycol backbone.The starting weight loss temperature of the three molecular weight polyethylene glycol bridged hindered phenol polymeric antioxidants was measured by thermogravimetry(TG)to be above 230℃,which proved that the synthesized series of polyethylene glycol bridged hindered phenols have good thermal stability.The antioxidant activity of the scavenging of reactive radicals by the DPPH method and the online oxygen measurement method was investigated,and the results showed that the synthesized series of polyethylene glycol bridged hindered phenolic polymeric antioxidants all had a good scavenging ability,and their scavenging activity increased with the increase of phenolic hydroxyl concentration.The scavenging efficiency of the series antioxidants was negatively correlated with the length of the bridged group when the scavenging reaction time was 30 min.As the length of the bridged group of the series of antioxidants increased,the scavenging activity of ROO·decreased accordingly.The melt flow rate,oxidation induction period,tensile property test,and migration resistance test were conducted to evaluate the antioxidant performance of the series polyethylene glycol bridged hindered phenolic polymeric antioxidants in metallocene linear low-density polyethylene(mLLDPE)system.The results showed that the series polyethylene glycol bridged hindered phenolic polymeic antioxidants and could better inhibit the thermal-oxidative aging degradation of mLLDPE.The melt flow rate of mLLDPE with the addition of the series of antioxidants increased and the oxidation induction period decreased with the increase of the length of the bridged group.A series of polyethylene glycol bridged hindered phenolic polymeric antioxidants on mLLDPE tensile yield strength is not significant,with the increase in the length of the bridged group,the addition of a series of antioxidants mLLDPE tensile properties decreased.Compared with Irganox 1098,a series of polyethylene glycol bridged hindered phenolic polymeric antioxidants have stronger migration resistance,and with the increase in the length of the bridged group,the stronger the migration resistance of the series of antioxidants.