The antioxidant performance of a sterically hindered bisphenol antioxidant, 4,4'-bis(2,6-di-tert-butylphenol), in model reactions of accelerated aging of carbon-chain polymers (polypropylene, isoprene rubber) was studied. This antioxidant was examined by differential scanning calorimetry and Wallace plasticity measurements in comparison with known commercial phenolic and amine stabilizers. High performance of 4,4'-bis(2,6-di-tertbutylphenol) as antioxidant was revealed.

No abstract

No abstract

An efficient procedure was developed for preparing bis (3,5-di-tert-butyl-4-hydroxyphenyl) polysulfides in the presence of phenolic Mannich bases. The antioxidative activity of the resulting bis(polysulfides) in rubbers of various structures and in their vulcanizates was examined.Sterically hindered phenols (SHPs) find growing use for antioxidative stabilization of polymeric materials, thanks to the strong protective effect of SHPs and their low toxicity. Today the researchers' attention is focused on molecular structures containing, along with an SHP moiety, also additional groups or atoms suppressing the radical-chain oxidation in various steps and by different mechanisms [1, 2]. Such stabilizers can exhibit intramolecular synergism and substantially surpass in the antioxidative performance classical mixed synergistic stabilizing systems [1]. Among polyfunctional SHP antioxidants are compounds containing simultaneously SHP fragments and sulfide groups [1, 3].SHP sulfides were prepared previously by reactions of 2,6-dialkylphenols with S 2 Cl 2 and SCl 2 [4]. However, this route has certain disadvantages: relatively low yield of the target product, formation of a large amount of the by-product, and release of hydrogen chloride contaminated with sulfur chlorides. SHP polysulfides can also be prepared using elemental sulfur. According to [5], the reactions of SHPs with sulfur are performed in the presence of an at least equimolar amount of alkali relative to 2,6-dialkylphenol and of a large excess of sulfur. This makes the process technologically unfeasible, because of the necessity of utilizing large amounts of acidic aqueousorganic wastes. However, the procedure for preparing SHP polysulfides using elemental sulfur is attractive in connection with the pressing problem of utilization of [gas] sulfur, a by-product of hydrorefining of crude oil and hydrocarbon raw materials.The goals of this study were to develop a feasible procedure for preparing sterically hindered phenol sulfides by the reaction of 2,6-dialkylphenol with elemental sulfur and to examine their antioxidative (AO) performance in various rubbers and polymeric materials based on them. EXPERIMENTALThe following chemicals were used in the study.2,6-Di-tert-butylphenol. White crystals, mp 36 3 37oC, MW 206. Readily soluble in benzene, acetone, and isopropanol.Sulfur. mp 112.8oC, density 1960 32070 kg m !3 .A yellow crystalline solid, insoluble in water, sparingly soluble in alcohol and ether, and readily soluble in carbon disulfide. The molecular weight of sulfur at low temperatures corresponds to the formula S 8 . 2-Dimethylaminomethylphenol.A light yellow liquid; it contained a 1.88% impurity of phenol.2,6-Bis(dimethylaminomethyl)phenol. A light yellow liquid; it contained a 2.4% impurity of phenol. 4-Dimethylaminomethyl-2,6-di-tert-butylphenol. mp 93395oC (from acetone). MW 263. White or slightly yellowish crystals soluble in the majority of organic solvents.