Synthesis And Oxidative Stability Of Novel Semi-hindered Phenolic Antioxidants

The important intermediate methyl β-(3-methyl-5-tert-butyl-4-hydroxyphenyl)propanoate of semi-hindered phenolic antioxidants was successfully synthesized using 2-methyl-6-tert-butylphenol and methyl acrylate as materials and using potassium hydroxide as catalyst.The optimal synthesis system and synthetic process of β-(3-methyl-5-tert-butyl-4-hydroxyphenyl)propanoate were investigated through condition optimization experiments.Under the optimal condition,the yield of β-(3-methyl-5-tertbutyl-4-hydroxyphenyl)propanoate was more than 90%.Three novel semi-hindered phenolic antioxidants were synthesized with hexylenediamine,p-phenylenediamine and 1.0 generation dendrimer(1.0 G)as bridged groups and using β-(3-methyl-5-tert-butyl-4-hydroxyphenyl)propionyl chloride as antioxidant group.The structures of semi-hindered phenolic antioxidants were characterized by FT-IR,1H NMR and MS and the results indicated that the structures of semi-hindered phenolic antioxidants were consistent with the theoretical structures.The free radical scavenging capacities of three novel semi-hindered phenols were invesgated by DPPH assay,and the results indicated that the semi-hindered phenolic antioxidants could scavenge free radical rapidly and the scavenge reaction reached equilibrium in about 25 minutes.At the same time,the reaction rate and antioxidant efficiency of semi-hindered phenolic antioxidants were higher than those of the corresponding fully hindered phenolic antioxidants.The order of free radical scavenging capacity was: C6-1.0G dendrime macromolecule bridged semi-hindered phenol > p-phenylenediamine bridged semi-hindered phenol > hexanediamine bridged semi-hindered phenol.The thermooxidative stabilities of polyolefins with the three novel semi-hindered phenols were assessed by the measurement of oxidative induction temperature,carbonyl index and tensile strength.The results showed that three kinds of semi-hindered phenolic antioxidants increased the oxidative induction temperature of polyethylene and polypropylene.The oxidative induction temperature of polyethylene and polypropylene with p-phenylenediamine bridged semi-hindered phenolic antioxidants increased by 33 °C and 28 °C.After 105 days of aging test,the carbonyl index of polyethylene was 0.265,and the carbonyl index of polyethylene with three kinds of semi-hindered phenolic antioxidants was only 0.11.The tensile strength of polyethylene dramatically reduced from 29.6 MPa to 2.1 MPa after 105 days aging and the tensile strength of polyethylene with three kinds of semi-hindered phenols only reduced by 3 MPa.Polypropylene cracked aging for 45 days,while polypropylene containing the semi-hindered phenolic antioxidants had good tensile strength,which was because the semi-hindered phenoic antioxidants could scavenge free radicals rapidly and inhibit the degradation of polyolefins.The oxidative induction temperature of polyolefins increased with the increase of concentration of semi-hindered phenolic antioxidants.At the same concentration,the oxidative induction temperature of polyolefins containing different semi-hindered phenolic antoxidants was in the order of p-phenylenediamine bridged semi-hindered phenolic antioxidant > hexanediamine bridged semi-hindered phenolic antioxidant > C6-1.0G dendrime macromolecule bridged semi-hindered phenolic antioxidant.In addition,the semi-hindered phenolic antioxidants with Irganox 168 showed a good synergistic effect.