Design And Synthesis Of Composite Macromolecular Antioxidant For Nylon

To address the problem of migration of commonly used antioxidants in PA6,this project is designed to synthesize functionalized small molecule antioxidant of 3-（3,5-di-tert-butyl-4-hydroxyphenyl）propionic acid acrylamide methyl ester（AHP） containing hindered phenol,carbon-carbon double bond and benzene ring;using free radical copolymerization method,AHP was reacted with NPMI to synthesize macromolecular composite antioxidant poly（（3,5-di-tert-butyl-4-hydroxyphenyl）propionic acid acrylamide methyl ester-alt-N-phenylmaleimide）（PAN and Macro-PAN）with the same molecular structure units but different molecular weight.The structures of antioxidants AHP and PAN were characterized by FT-IR,NMR and HRMS,and the activity of antioxidants in scavenging 1,1-Diphenyl-2-picrylhydrazyl radical 2,2-Diphenyl-1-（2,4,6-trinitrophenyl）hydrazyl（DPPH）was evaluated using the free radical scavenging method.By employing PA6/PAN composites as a research sample model,the ability of the macromolecular composite antioxidant PAN to inhibit PA6 aging and its mechanism of action in PA6 were investigated by using migration resistance,△E test,TGA and mechanical property analysis,which provide a new way for the design and synthesis of new functionalized macromolecular antioxidants.The conclusions of the paper are as follows:（1）AHP,a small molecule antioxidant containing carbon-carbon double bond,was synthesized;PAN and Macro-PAN,a macromolecular composite antioxidant for PA6containing hindered phenols and tertiary amines,were synthesized.The molecular units structures of the PAN and Macro-PAN were the same but the Mn was different,with6575 g/mol for PAN and 11720 g/mol for Macro-PAN.（2）The antioxidant activity of the antioxidants PAN,Macro-PAN and 1010 was investigated using DPPH scavenging experiments,and the results showed that PAN has the highest antioxidant activity.By analyzing the radical scavenging rate versus time curves and EC₅₀,the factors affecting the antioxidant activity were proposed:Molecular weight affects the short-term clearance of DPPH by antioxidants,but has no effect on the total amount of scavenged;the type of antioxidant groups affects the total amount of radical scavenging by the antioxidant,which is the most important factor in determining the antioxidant activity.The macromolecular composite antioxidant PAN synthesized in this thesis contains dual antioxidant functional groups-hindered phenol and tertiary amine,and its antioxidant activity is higher than that of single antioxidant functional group antioxidant 1010.（3）PA6/1010 and PA6/PAN composites were prepared by adding 5 wt.‰of antioxidants with different molecular weights,and their migration resistance,yellowing resistance index and mechanical properties were characterized.After shaking the PA6composites in ethanol for 96 h,the migration rate of the macromolecular composite antioxidant PAN was only 28%of that of the antioxidant 1010;After 12-day accelerated thermal oxygen aging test in an oven at 150°C,The△E between pure PA6,PA6/1010and PA6/PAN composites with and without aging were 28.4,26.7 and 14.3,respectively.This indicates that the addition of antioxidant can effectively inhibit the color change of the material,and the yellowing resistance of antioxidant PAN is much higher than that of antioxidant 1010.In addition,the results of DSC,DMA and rheology are consistent with the results of yellowing resistance.Experiments have confirmed the effectiveness of large molecular weight inhibition of antioxidant PAN migration,which can achieve the purpose of delaying the aging of PA6.（4）Analyzed antioxidant PAN scavenging DPPH mechanism and its long-lasting anti-thermal oxygen aging effect in PA6,proposed the mechanism of action of macromolecular composite antioxidant PAN in PA6:the hindered phenol group and tertiary amine group provide hydrogen atom and lone electron,respectively,and the two antioxidant groups react with highly reactive peroxyl radicals that generated by PA6 molecular chain break,so that the radicals are converted into stable state structure.The two antioxidant groups work together to improve the long-lasting antioxidant performance of PA6.