Synthesis Of Hydroxyl Terminated Polybutadiene Bound2,2’-Methylene (or2,2-Thio)bis(4-methyl-6-tert-butylphenol) And Their Thermo-Oxidative Aging Resistance For Natural Rubber

Polymers are easy to suffer from uncontrolled oxidation in the process of storage, processing and using because of the effects of heat, oxygen, ozone, mechanical stress and so on. It results in crosslinking or degradation of the molecular chain, and leads to deteriorate in structure and properties to lose use value. The phenomenon is referred to as the oxidative aging of the polymer. The oxidative aging is severe especially for rubbers containing a large amount of unsaturated C=C bonds in their molecular chain. In order to prevent or retard oxidative reaction, various antioxidants are usually added into the polymers. However, low molecular weight antioxidants are easy to volatilize, migrate, or be extracted from the polymer substrate, which makes the thermo-oxidative aging resistance of polymer worse and could results in environment pollution. In recent years, polymeric antioxidant has increasingly attracted attention in order to avoid the loss of antioxidant from the substrate. In this dissertation, two kinds of novel polymeric antioxidants hydroxyl terminated polybutadiene bound2,2’-methylenebis (4-methyl-6-tert-butylphenol) or2,2’-thiobis (4-methyl-6-tert-butylphenol)(HTPB-IPDI-MPH or HTPB-IPDI-TPH) were prepared through isophorone diisocyanate (IPDI) as bridging agent. The effect of HTPB-IPDI-MPH and HTPB-IPDI-TPH on thermo-oxidative aging resistance for NR vulcanizates and their extraction resistance were investigated, and the mechanism of thermo-oxidative aging resistance was discussed. The main research contents and results are listed as following:Firstly, two kinds of novel polymeric antioxidants HTPB-IPDI-MPH and HTPB-IPDI-TPH were synthesized by the reactions between2,2-methylenebis (4-methyl-6-tert-butylphenol)(MPH) or2,2’-thiobis (4-methyl-6-tert-butylphenol)(TPH) and an adduct (HTPB-IPDI) from hydroxyl terminated polybutadiene (HTPB) and isophorone diisocyanate (IPDI). The effects of reactants ratio and the reaction condition on the reaction were investigated by measuring the content of the residual-NCO groups of the reactants during the reaction. The optimal reaction condition between IPDI and HTPB was that the amount of dibutyltin dilaurate (DBTDL) was0.6wt%based on IPDI, and the temperature and time were40℃and270min, respectively. The reaction condition between MPH or TPH and HTPB-IPDI was that the molar ratio of MPH or TPH to-NCO in HTPB-IPDI was3:1, and the amount of DBTDL was1.6wt%based on the total of reactants, and the temperature and time were75℃and360min, respectively. The content of the residual-NCO groups of the reactants were0.29wt%or0.43wt%under this condition, respectively.Secondly, the structures of HTPB-IPDI-MPH and HTPB-IPDI-TPH were characterized by FT-IR,1H-NMR,13C-NMR and GPC, and the thermal stability of HTPB-IPDI-MPH and HTPB-IPDI-TPH was investigated by TGA. The results showed that only one of phenolic-OH in MPH or TPH reacted with-NCO in HTPB-IPDI, while another phenolic-OH in MPH or TPH remained in HTPB-IPDI-MPH and HTPB-IPDI-TPH, respectively. The thermal stability of HTPB-IPDI-MPH and HTPB-IPDI-TPH were obviously superior to corresponding low molecualar weigth antioxidant MPH and TPH, respectively.Thirdly, the effect of HTPB-IPDI-MPH and HTPB-IPDI-TPH on curing characteristics and processing properties of NR compounds, mechanical properties and dynamic viscoelastic properties of NR vulcanizates were investigated. The results showed that HTPB-IPDI-MPH and HTPB-IPDI-TPH could promote the vulcanization, but the effect of HTPB-IPDI-MPH and HTPB-IPDI-TPH on mechnical properties of NR vulcanizates was slight. The NR vulcanizates with HTPB-IPDI-MPH and HTPB-IPDI-TPH exhibited more obvious payne effect than that of the low molecular weight antioxidant MPH and TPH.Fourthly, the effect of HTPB-IPDI-MPH and HTPB-IPDI-TPH on the thermo-oxidative aging resistance was investigated, and the mechanism of thermo-oxidative aging resistance was discussed combining with results of FTIR-ATR spectra. The results showed that the thermo-oxidative aging resistance of NR vulcanizates with HTPB-IPDI-MPH and HTPB-IPDI-TPH were superior to that of MPH and TPH. Compared with hydroxyl terminated polybutadiene bound2,6-dibutyl-4-methylphenol (HTPB-IPDI-BHT),2,2’-methylenebis (4-methyl-6-tert-butylphenol) dodecanoic acid ester (MPH-DA) and2,2’-thiobis (4-methyl-6-tert-butylphenol) dodecanoic acid ester (TPH-DA) which were synthesized by our team, it was found that-NHCOO-groups in HTPB-IPDI-MPH and HTPB-IPDI-TPH had thermo-oxidatve aging resistance and synergistic effect with phenolic hydroxy group.Lastly, the extraction resistance of NR vulcanizates with HTPB-IPDI-MPH and HTPB-IPDI-TPH was investigated by compared with MPH, TPH, dodecanol bound2,2’-methylenebis (4-methyl-6-tert-butylphenol)(DN-IPDI-MPH) and dodecanol bound2,2-thiobis (4-methyl-6-tert-butylphenol)(DN-IPDI-TPH). The results showed that HTPB-IPDI-MPH and HTPB-IPDI-TPH had excellent extraction resistance. The aging coefficien of the NR vulcanizates with HTPB-IPDI-MPH and HTPB-IPDI-TPH which was extracted in100℃boiling water were0.55and0.56after aging at100℃for48h, respectively. The aging coefficien of DN-IPDI-MPH and DN-IPDI-TPH were0.37and0.41, respectively, while the aging coefficien of MPH and TPH were0.28and0.34, respectively. The aging coefficien of the NR vulcanizates with HTPB-IPDI-MPH and HTPB-IPDI-TPH which was extracted in methanol were0.44and0.48after aging at100℃for48h, respectively. The aging coefficien of DN-IPDI-MPH and DN-IPDI-TPH were0.40and0.39, respectively, while the aging coefficien of MPH and TPH were0.36.