Synthesis and reactivity of antioxidants based on vernolic acid and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid

The reactivity of sterically hindered phenols toward free radicals of the hydrocarbon cumene was studied. New compounds, i. e. methyl cis-13(12)-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}-12(13)-hydroxyoleate and cis-13(12)-{3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxy}-12(13)-hydroxyoleic acid were synthesized starting from vernolic acid and its methyl ester, respectively, and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid. Both new compounds possess antioxidant activities similar to those of commercially available antioxidants.     

Melt free‐radical grafting of maleimides with hindered phenol groups onto polyethylene

A monomeric antioxidant, bearing carbamate groups, was synthesized from the reaction of 3,5‐di‐tert‐butyl‐4‐hydroxybenzyl alcohol and azidomaleimide. Another antioxidant was prepared from the reaction of N‐(4‐hydroxyphenyl)maleimide and 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl) propionic chloride in the presence of triethylamine. These fictional antioxidants were grafted onto polyethylene (PE) via melt processing with free‐radical initiators in a minimax molder. The IR spectra of the grafted PE showed that the monomeric antioxidants were added to PE. IR spectroscopy methods were used for the quantitative determination of the extent of grafting of the monomeric antioxidants. Also, the extent of crosslinking was determined from the gel content. To optimize the reaction conditions, we investigated the effects of the initiator concentration, monomeric antioxidant, reaction time, and temperature on the extent of grafting. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2117–2122, 2004     

Studies on antioxidants. III. 2[(3,5-di-tert-butyl-4-hydroxyphenyl)methylene]hydrazine carbothioamide as a melt stabilizer for unstabilized polypropylene

Polypropylene's high processing temperatures initiate thermal oxidative degradation and loss of physical properties. Antioxidants protect polymers through the severe conditions of processing and fabrication and also through end use. Small amounts of antioxidants like 2,6-di-tert-butyl-4-methylphenol and 2[(3,5-di-tert-butyl-4-hydroxyphenyl)methylenel]-hydrazine carbothioamide are shown to be effective in protecting isotactic polypropylene (IPP) against thermooxidative degradation. 2[3,5-Di-tert-butyl-4-hydroxyphenyl)-methylene]hydrazine carbothioamide was melt compounded with IPP using a twin screw extruder. The melt flow index of the extruded sample was measured. The extruded granules were injection molded to get specimens suitable for testing mechanical properties, such as heat deflection temperature, Izod impact strength, tensile strength, tensile modulus, flexural strength, and flexural modulus. 2[(3,5-Di-tert-butyl-4-hydroxyphenyl)methylene]hydrazine carbothioamide was found to be an effective melt stabilizer for unstabilized polypropylene. © 1995 John Wiley & Sons, Inc.     

Stabilization of high-density polyethylene

Several types of antioxidants are evaluated in high-density polyethylene for color and physical property stabilization during processing and thermal aging. A wide variety of evaluation tests are used and discussed. Heat- and light-induced oxidation mechanisms are reviewed. Antioxidants such as octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and tetrakis[methylene 3-(3′,5′-di-tert-butyl-4′-hydroxy phenyl) propionate] methane were found to provide very high retention of physical properties, excellent initial color and color retention. Combinations of antioxidant- and ultraviolet light absorbers were evaluated for stabilizing high density polyethylene exposed to artificial light and outdoor weathering. The combination of octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate and 2-(2′-5′-di-tert-butyl-2′-hydroxy-phenyl)-5-chlorobenzotriazole was found to be a very efficient stabilizer system. Polymer containing this stabilizer combination had excellent color stability and minimum crosslinking and embrittlement after Arizona weathering.     

Antioxidant synergism between butylated hydroxyanisole and butylated hydroxytoluene

Decay of the 2,6-di-tert-butyl-4-methylphenoxy radical [butylated hydroxytoluene (BHT)-radical] in the presence of butylated hydroxyanisole (BHA) was investigated in 1,2-dimethoxyethane with or without triethylamine. BHT-radical was conveniently generated by dissociation of its unstable dimer in solution. The products were BHT, 3,3′-di-tert-butyl-5,5′-dimethoxy-2,2′-dihydroxybiphenyl (BHA-dimer), 2,6-di-tert-butyl-p-quinone methide (QM), 1,2-bis(3,5-di-tert-butyl-4-hydroxyphenyl)ethane, and 3,3′,5,5′-tetra-tert-butyl-4,4′-stilbenequinone. The reaction without added triethylamine gave larger quantities of the last two products and BHA (recovery), whereas the reaction with it provided larger quantities of the first two products. The marked difference in the product distribution can be accounted for by a series of reactions including reversible dehydrogenation of BHA with BHT-radical, which generates 2-tert-butyl-4-methoxyphenoxy radical (BHA-radical) and BHT, reversible dimerization of BHA-radical, which affords an intermediarybis(cyclohexadienone), and spontaneous and base-catalyzed prototropic rearrangement of the intermediate into BHA-dimer. Products of coupling between BHT-radical and BHA-radical were not obtained. BHA was found to undergo facile acid-catalyzed addition to QM, providing two isomericbis(hydroxyphenyl)methanes. The results help to elucidate the mechanism of antioxidant synergism between BHA and BHT and may suggest that the synergism can be affected by base or acid.     

Studies of tetrazoles as rubber chemicals. I. Preparation and characterization of reactive antioxidants based on tetrazoles

The novel reactive antioxidants based on tetrazoles that are stable at room temperature and convertible into the highly reactive nitrileimines by pyrolysis were prepared and the reactivity for carbon–carbon double bonds was evaluated. Antioxidants, i.e., 2-substituted phenyl-5-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)tetrazoles (PHPT) were prepared with the reaction of p-toluenesulfonylhydrazone of 3,5-di-tert-butyl-4-hydroxybenzaldehyde and substituted phenyl diazonium chloride in a mixed solvent of pyridine, ethanol, and water at ?10°C to ?20°C in 31-61% yields. To evaluate the reactivities of PHPT for carbon–carbon double bonds, m-chloro-substituted PHPT was pyrolyzed in an excess of styrene at 160–170°C for 0.5 h to give the 1-(3′-chlorophenyl)-3-(3″,5″-di-tert-butyl-4″-hydroxyphenyl)-5-phenyl-2-pyridazoline in a 44.1% yield by 1,3-dipolar addition reaction of the nitrileimine formed from the m-chloro-substituted PHPT. The thermogravimetric analysis of a mixture of proton isomer of PHPT and liquid polybutadiene showed that PHPT attached to liquid polybutadiene with an accompanying evolution of nitrogen.     

A new approach to quantitatively assessing the effects of polymer additives

A novel approach involving stability parameter mapping and stability vector analysis is developed for assessing the effect of an additive on polymer performance. The potential usefulness of the method is illustrated by applying it to (i) DSC oxidative induction time (OIt) data for medium-density polyethylene (MDPE) formulations made using two levels of carbon black and base-stabilized with Irgafos 168™ (tris-(2,4-di-tert-butylphenyl)-phosphite) and Irganox 1010™ pentaerythrityl-tetrakis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), and (ii) chemiluminescence OIt data for low-density polyethylene (LDPE) containing 0.2% (w/w) of Chimassorb 944™ and 0.5% (w/w) or 1.0% (w/w) of dicumyl peroxide cross-linking agent and base-stabilized with 0.2% (w/w) of various commercial antioxidants. The proposed method is validated using data from a previous study on MDPE and is applied to a preliminary investigation of LDPE destabilization by dicumyl peroxide. The results suggest that a styrenated phenolic stabilizer blended with zinc dibutyldithiocarbamate and zinc stearate is an effective system for stabilizing LDPE in the presence of dicumyl peroxide.     

Gamma-ray induced crosslinking of polynorbornene and its copolymer containing a stabilizing group

Summary The gamma-ray induced, solid state crosslinking of polynorbornene(PolyNB) and its copolymer was studied. PolyNB degradates when irradiated in air, but it is readily crosslinked in vacuum. Homopolymer and copolymers containing a stabilizing group, 3,5-di-tert-butyl-4-hydroxybenzoyloxy group, were resistant to crosslinking showing induction periods before crosslinking. The irradiated PolyNB showed an ESR signal due to the allyl radical, and the polymer containing the hydroxybenzoyloxy group showed a signal due to the quinolic radical.     

Commercial antioxidants as photostabilizers for butadiene rubber

In this work we have studied the stabilizing effect of several commercially available antioxidants on the free-radical photooxidation of butadiene rubber. Two kinds of stabilizers were investigated; hindered phenols: 2,4-di-t-butyl-p-hydroxytoluene, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate and 2,4-bis(octylthio)-6-(4-hydroxy-3,5-di-t-butylanilino)-1,3,5-triazine; and amine stabilizers: N-isopropyl-N′-phenyl-p-phenylenediamine and N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine. Their stabilizing effect is mostly produced by scavenging the peroxy radicals formed during the initial steps of the photodegradation process. We also tested tri(nonylphenyl)phosphite associated with the phenoltriazine stabilizer. Of the additives studied in this work, octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate was the most effective photostabilizer for butadiene rubber.     

Organic/inorganic hybrid composites prepared by polymerization compounding and controlled free radical polymerization

A new method to produce highly filled and well dispersed polymer solid composites using controlled free radical polymerization has been developed. Grafting of polymers onto ultrafine silica was done in bulk polymerization at 120 °C in presence of N-tert-butyl-1-diethylphosphono2,2-dimethyl propyl nitroxide (DEPN) as a nitroxide stable free radical. Optimum conditions for tert-butyl hydroperoxide grafting onto fumed silica were first determined. The percentage of grafting, the architecture of grafted polymers, the length of chains, and the polydispersity index can be controlled at will using this approach. The effect of the number of grafted polymer chains combined with its molecular weight on the processing of these materials was investigated. The syntheses performed in this work gave grafting percentages of polymers and copolymers ranging from 12 to 88 wt%. All ‘synthesized’ composites gave stable suspensions in toluene and tetrahydrofuran.     

Melt free‐radical grafting of hindered phenol antioxidant onto polyethylene

A monomeric antioxidant (3) was prepared by reacting 3,5‐di‐tert‐butyl‐4‐hydroxybenzyl alcohol (1) with N‐[4‐(chlorocarbonyl) phenyl] maleimide (2). This reactive antioxidant was grafted onto polyethylene (PE) by melt processing with free‐radical initiators in a mini‐max molder. The IR spectra of the grafted PE showed that the monomeric antioxidant was introduced onto the PE. IR spectroscopic methods and titration were used for the quantitative determination of the extent of grafting of the monomeric antioxidant. Also, the extent of crosslinking was indicated by the gel content. Grafting occurred in the following order: dicumyl peroxide (DCP) > benzoyl peroxide > 2,2′‐azobisisobutyronitrile. The influences of the DCP concentration and monomeric antioxidant on the extent of grafting were studied. The effects of the reaction time and temperature were also determined. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2968–2973, 2000     

An FTIR solid-state analysis of the diffusion of hindered phenols in low-density polyethylene (LDPE): The effect of molecular size on the diffusion coefficient

Low-density polyethylene (LDPE) has been investigated with respect to the diffusion of hindered phenol antioxidants added to the polymer matrix. In the study, a simple method was used to measure the diffusion coeficient, with the aid of FTIR spectroscopy without any extraction or refining steps in the analysis. The diffusion coefficient, D, of five phenols containing the same 3(3,5-di-tert-butyl-4-hydroxyphenyl) structure but with different lengths of the hydrocarbon tail were obtained in the temperature range 30–60°C. The number of carbon atoms in the tail varied between 1 and 18. It was found that the logarithm of D decreased linearly with increasing molecular size. The temperature-dependence of the phenols could be described by an Arrhenius-type relationship. It was found that the activation energy, E_d, incresed linearly with increasing molecular size. © 1994 John Wiley & Sons, Inc.     

Effects of phenolic antioxidants on ultrahigh molecular weight polyethylene/decalin solution

The degradation of ultrahigh molecular weight polyethylene (UHMW‐PE) during its dissolution into decalin is discussed. The stabilization of the solution by three phenolic antioxidants, octadecyl β‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propionate (1076), tetrakis[methylene‐β‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propionate]methane (1010), and 1,1,3‐tris(2‐methyl‐4‐hydroxy‐5‐tert‐butylphenyl)butane (CA), and an auxiliary antioxidant, dilaurylthiodipropionate (DLTP) is also discussed. Among the three phenolic antioxidants, 1076 had the greatest effect. The auxiliary antioxidant was effective in stabilizing the solution when combined with one of the three phenolic antioxidants. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2877–2881, 2000     

A study of radical graft copolymerization on polypropylene during extrusion using two peroxide initiators

Functionalization of polypropylene (PP) during melt extrusion has been explored extensively. In this study, two different radical initiators were employed and compared in grafting acyclic halamine precursors to PP. 2,4‐Diamino‐6‐diallylamino‐1,3,5‐triazine (NDAM) was grafted onto PP during a melt‐extrusion process using either 2,5‐dimethyl‐2,5‐(tert‐butylperoxy)hexyne (DTBHY) or dicumyl peroxide (DCP) as initiator. The results confirmed the radical graft copolymerization of the monomer onto the PP backbone during the reactive extrusion process. It was revealed that, at low monomer concentration, when peroxide initiator concentration was increased, polymer chain scission became dominant. DCP was more efficient than DTBHY as an initiator in the graft polymerization. After exposure to chlorine bleach, the grafted structures could be easily transformed into N‐halamines, which provided powerful, durable and regenerable antibacterial activities against Escherichia coli and Staphylococcus aureus. It is concluded that both DCP and DTBHY could be used as radical initiators in reactive extrusion to graft certain vinyl monomers to PP. The NDAM‐grafted PP could provide expected antibacterial function after chlorination of the grafted product in a chlorine bleach solution. The modified PP showed great potential for use in medical devices and non‐woven textiles. Copyright © 2009 Society of Chemical Industry     

The catalytic activity of immobilized on modified silica metalloporphyrins bearing antioxidative 2,6-di-tert-butylphenol pendants

A comparative study of the catalytic activity of supported manganese(III) and iron(III) chlorides of meso-tetrakis(3,5-di-tert-butyl-4-hydroxyphenyl)porphyrin (R₄PMnCl, R₄PFeCl) and meso-tetraphenylporphyrin (TPPMnCl, TPPFeCl) is reported. The metalloporphyrins have been immobilized via coordination bond on the surface of two series of imidazole modified silica, imidazole propyl silica (IPS) and imidazole 3-(glycidyloxypropyl) silica (IGOPS). The heterogenised catalysts have been evaluated for hydrocarbon oxidation by sodium periodate. The critical role of 2,6-di-tert-butylphenol groups on the periphery of porphyrin ring in their catalytic activity has been evaluated and pertinent structural and mechanistic aspects are discussed.     

Synthesis and magnetic properties of polydiphenylamine derivative bearing stable radical groups

Poly[4,4′-diphenylamine (3,5-di-tert-butyl-4-hydroxy)benzylidene] was synthesized with a dehydrative polycondensation by using H₂SO₄ as a catalyst. After treatment with DDQ, the polymer was oxidized with PbO₂ to generate a stable radical group in the polymer. The colour of the polymer changed from green to dark red upon the oxidation. ESR spectra showed not only a signal with a g value of 2.004, but also a so-called ‘half-field’ signal with a g value of 4.288.     

Antioxidative activity of derivatives of vitamin B6 and structurally related compounds

Summary Fat-soluble derivatives of vitamin B₆ including ethylN-pyridoxyl-p-aminobenzoate, pyridoxal isonicotinoylhydrazone, and pyridoxine 5-monopalmitate showed little or no antioxidative activity for lard as well as for vitamin A at 37°C. The structurally related compounds, ethylN-vanillyl-p-aminobenzoate, vanillin isonicotinoylhydrazone, and the nicotinoylhydrazone were found to be antioxidants although free vanillin was inactive. The removal of the electron-withdrawing nature at the formyl group in a vanillin molecule might be functional in the development of antioxygenic properties. Evidence was obtained to show that an isonicotinoylhydrazonomethyl group not only activated a phenolic compound as an antioxidant but also removed pro-oxidative metallic ions from lard through chelation. For example, 3,5-di-tert-butyl-4-hydroxybenzaldehyde isonicotinoylhydrazone (BHB-INH), a structural analogue of butylated hydroxytoluene (BHT), stabilized lard more efficiently than BHT on a molar basis in the presence as well as in the absence of Cu⁺⁺. This work was supported by Research Grant No. A-257 from the National Institutes of Health, U. S. Public Health Service, Department of Health, Education, and Welfare. The term “pyridoxyl” denotes the 2-methyl-3-hydroxy-5-hydroxymethyl-4-pyridylmethyl radical. The term “pyridoxylidene” denotes the 2-methyl-3-hydroxy-5-hydroxymethyl-4-pyridylmethylene radical.     

Maleation of polylactide (PLA) by reactive extrusion

Free‐radical‐initiated grafting of maleic anhydride (MA) onto a polylactide (PLA) backbone was performed by reactive extrusion. A concentration of 2 wt % MA in the presence of 2,5‐dimethyl‐2,5‐di‐(tert‐butylperoxy)hexane (Lupersol 101) as the free‐radical initiator was used for all experiments. Two reaction temperatures were studied (180 and 200°C) with a peroxide initiator concentration between 0.0 and 0.5 wt %. Under these conditions, between 0.066 and 0.672 wt % MA was grafted onto the PLA chains. Triple‐detector size‐exclusion chromatography (TriSEC), melt flow index (MFI), and thermal gravimetric analysis (TGA) were used to characterize the maleated PLA polymers. Increasing the initiator concentration resulted in an increase in the grafting of MA, as well as a decrease in the molecular weight of the polymer. The maleation of PLA proved to be very efficient in promoting strong interfacial adhesion with corn native starch in composites as obtained by melt blending. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 477–485, 1999     

多乙烯多胺桥联受阻酚类抗氧剂的合成及其清除DPPH·性能

以二乙烯三胺和三乙烯四胺为桥联基,β-(3,5-二叔丁基-4-羟基苯基)丙酰氯为抗氧化功能基团,通过酰胺化缩合反应合成了两类具有不同对位桥联基团的受阻酚类抗氧剂。采用傅里叶红外光谱和核磁共振氢谱证实了合成的多乙烯多胺桥联受阻酚类抗氧剂的化学结构。DPPH法研究了多乙烯多胺桥联受阻酚类抗氧剂清除自由基的性能,并探索了酚羟基个数和对位桥联基结构对受阻酚类抗氧剂清除自由基性能的影响。结果表明,多乙烯多胺桥联受阻酚类抗氧剂具有良好的清除DPPH·能力,且随着抗氧剂分子中酚羟基个数的增加,清除DPPH·的活性增加,分子中含有4个酚羟基的三乙烯四胺受阻酚类抗氧剂的抗氧化效率（AE）达到2.65×10^-2 L/(mol·s)。对位桥联基结构对受阻酚类抗氧剂清除DPPH·能力有较大影响,季戊四醇为桥联基的受阻酚类抗氧剂1010清除DPPH·能力最强,其抗氧化效率（AE）为3.08×10^-2L/(mol·s);乙二胺为核的1.0代树枝状受阻酚类抗氧剂清除DPPH·能力最弱,其抗氧化效率（AE）为2.60×10^-2 L/(mol·s)。     

Graft copolymerization studies. III. Methyl methacrylate onto polypropylene and polyethylene terephthalate

The tert‐butoxy radical‐facilitated grafting of methyl methacrylate (MMA) onto commercial polypropylene (PP) pellets and fiber was investigated in heterogeneous conditions similar to practical systems. Free‐radical grafting of several other monomers onto PP fiber was also investigated. Also, preliminary data from the grafting of MMA onto poly(ethylene terephthalate) pellets is presented. The PP‐graft‐PMMA residues were detected by solid‐state ¹³C‐NMR and photoacoustic IR spectroscopy. There was a good correlation between the degree of grafting (DG) determined from these spectroscopic techniques and the results from gravimetric methods. A maximum grafting efficiency of over 50% was found, whereas DG (20%) remained constant at various PP pellet, initiator, and monomer concentrations. However, at relatively low PP fiber concentrations, the DG was 27%; the increase was most likely due to the greater surface area of the fiber. There was also a reduction in DG (14%) at relatively low initiator concentrations. The reaction conditions were altered to favor grafting by the addition of more polymer substrate. When the ratio of tert‐butoxy radicals to PP was decreased, more of the substrate remained unmodified, and empirical calculations showed the formation of grafts with up to 40 monomer units. At high initiator concentrations, calculations showed that the graft residues were 1–2 units long. Therefore, variation of the polymer, initiator, and monomer concentrations was shown to have a significant effect on grafting. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 898–915, 2002