Polymeric Antioxidants Research Articles

Structural Characterization of Hydroxyl-Terminated Polybutadiene-Bound 2, 2-Thiobis(4-methyl-6-tert-butylphenol) and Its Thermo-Oxidative Aging Resistance for Natural Rubber Vulcanizates

A novel polymeric antioxidant, hydroxyl-terminated polybutadiene-bound 2,2-thiobis(4-methyl-6-tert-butylphenol) (HTPB-IPDI-TPH), was prepared by binding 2, 2-thiobis(4-methyl-6-tert-butylphenol) (TPH) onto hydroxyl-terminated polybutadiene (HTPB) with isophorone diisocyanate (IPDI). Fourier-transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance spectroscopy (13C NMR), and gel permeation chromatography (GPC) were used to characterize the structure of HTPB-IPDI-TPH. The thermal stability of HTPB-IPDI-TPH was studied by thermogravimetry analysis (TGA). The effect of HTPB-IPDI-TPH on thermo-oxidative aging resistance of NR vulcanizates was investigated, and the mechanism of thermo-oxidative aging resistance was preliminarily discussed. The results showed that HTPB-IPDI-TPH contributed better thermal stability and thermo-oxidative aging resistance to NR vulcanizates than TPH. The thermo-oxidative aging resistance of HTPB-IPDI-TPH was more remarkable in the later stage of aging. Attenuated total-reflectance Fourier-transform infrared spectroscopy (FTIR-ATR) analysis showed that the relative content of carbonyl groups of NR vulcanizate with HTPB-IPDI-TPH was obviously lower than that with TPH after thermo-oxidative aging. It is suggested that ‒NHCOO‒ groups in HTPB-IPDI-TPH enhanced the ability of trapping alkyl peroxide radicals.

LDPE‐based blends and films stabilized with nonreleasing polymeric antioxidants for safer food packaging

AbstractSeveral novel random copolymers of ethylene and 1‐olefin counits bearing a highly efficient phenolic antioxidant moiety placed at different distances from the polymerizable double bond were prepared in the presence of a metallocene catalyst. These copolymers were melt‐blended with an antioxidant‐free LDPE in an internal batch mixer to obtain innovative materials containing nonreleasing polymeric antioxidants suitable for safer food packaging applications. Blends and films, obtained by compression molding, were tested for their thermal and thermo‐oxidative stability by thermogravimetric analysis both in dynamic and isothermal conditions. Films containing the macromolecular antioxidants showed a longer induction time before O2 uptake starts and, consequently, a higher degradation temperature than neat LDPE or LDPE containing a low molecular weight commercial additive. Aging tests demonstrated that the new polymeric antioxidants also exert a valid protection against photo‐oxidation. Eventually, migration tests demonstrated the absence of any trace of products containing the antioxidant moiety when the films were kept in contact with a food simulant. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis and the Characterizations of Structure and Function of Gallic Acid Microcrystalline Cellulose Ester

In order to solve the toxicity problem of gallic acid and its esters as food antioxidant,using the advantages of microcrystalline cellulose security and not to be absorbed by the body, a new type of polymeric anti-oxidants was exploited. Gallic acid microcrystalline cellulose ester was prepared by indirect esterification method ,which gallic acid and microcrystalline cellulose were used as raw materials. The structures of reaction materials and products were characterized and its oxidation resistance, stability, acute toxicology were studied by infrared spectroscopy, X-ray diffraction spectroscopy, scanning electron microscopy .The results showed that: gallic acid microcrystalline cellulose ester was successfully synthesized ; its ability to remove all kinds of free radicals was higher than or approximate equal to gallic acid; suitable for room temperature storage, high temperature sterilization, ultraviolet sterilizer, pH3.0~9.0,under these conditions it was stability;it was non-toxic substance, the safety was higher than gallic acid and gallic acid propyl. This study established the technical foundation for the further development of a new type of functional macromolecular compound which could be used for antioxidation.

Phenolic Antioxidant for Polyolefins from Grafted Phenol on Polyethylene Wax

AbstractSummery: This study consists of the preparation of a new polymeric antioxidant from the grafting of phenol on the backbone of chlorinated polyethylene wax by alkylation's reaction in the presence of AlCl3 as catalyst. The chemical structure of the prepared phenolic polyethylene wax(ph ‐ wax) was characterized by FTIR. The thermal oxidation of HDPE was examined by monitoring the amount of O2 uptake by samples of HDPE with the (ph‐wax) volumetrically at 230 °C, also the thermal oxidation degradation of HDPE with the (ph‐wax) derivative was studied by monitoring the weight loss of the samples during heating at 250 °C and under normal air as atmosphere. The results of this study show a decrease in the rate of HDPE oxidation in the presence of ph‐wax at four percent (0.2, 0.4, 0.6 and 0.8) %wt/wt of polymer, while the oxidation time of HDPE increased from (5) min. for pure HDPE to reach (41) min. for (0.8) % sample. The thermograms and thermal data of this study indicate that the stability of HDPE increases with the percent of the (ph‐wax) (0.6 and 0.8) wt/wt%. Generally, these results show that phenolic wax has excellent performance as an antioxidant for polyethylene.

Synthesis of polymeric antioxidants based on ring-opening metathesis polymerization (ROMP) and their antioxidant ability for preventing polypropylene (PP) from thermal oxidation degradation

Norbornene derivatives 1– 5 bearing hindered phenol groups were synthesized and undergone ring-opening metathesis polymerization (ROMP) with Grubbs 1st generation catalyst to prepare the corresponding polymeric antioxidants. After hydrogenation with p-toluenesulfonylhydrazide (TSH), polymeric antioxidants with saturated polymer chain were prepared. The resulting polymeric antioxidants were characterized by gel permeation chromatography (GPC), 1H NMR and differential scanning calorimetry (DSC). As to polymerization activity, monomer 1 had the highest ROMP activity, while monomer 5 could not undergo homopolymerization due to the steric hindrance. The antioxidant ability of these polymeric antioxidants which was determined by oxidation induction temperature (OIT) in polypropylene (PP) system is to protect PP against thermal oxidation. Results showed that the OIT of PP increased obviously when PP was stabilized by the adding of polymeric antioxidants.

Rubber Vulcanizates Degradation and Stabilization

Abstract Degradation of rubber vulcanizates in the presence and absence of air as well as in presence of ozone is reviewed in this paper. The paper also outlines the means to overcome this undesirable phenomenon. Under anaerobic aging conditions, which is termed as reversion, the vulcanizates are exposed to elevated temperature in the absence of oxygen. The consequence of this process is reflected in a decline in physical properties and performance characteristics. These changes are directly related to modifications of the original crosslink structure. Decomposition reactions tend to predominate and thus leading to a reduction in crosslink density and physical properties as observed during extended cure or when using higher curing temperatures. The decrease in network density is common when vulcanizates are subject to an anaerobic aging process. However, in the presence of oxygen, the network density is increased with the main chain modifications playing a vital role. Over the years the rubber industry has developed several compounding approaches to address the changes in crosslink structure during thermal aging. This paper gives a review of these compounding approaches. As with many formulation changes in rubber compounding, there is a compromise that must be made when attempting to improve one performance characteristic. For example, improving the thermal stability of vulcanized natural rubber compounds by reducing the sulfur content of the crosslink through the use of the more efficient vulcanization systems will reduce dynamic performance properties such as fatigue resistance. The challenge is to define a way to improve thermal stability while maintaining dynamic performance characteristics. In the second part, the protection against aerobic ageing as well as in ozone environment is reviewed. The anti-degradant effects are summarized and means to counteract are outlined. The most commonly used antidegradants are N-isopropyl-N′-phenyl-p-phenylenediamine (IPPD) and N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD). Although conventional antidegradants such as IPPD and 6PPD are still the most widely used antidegradants in rubber, there is a trend and demand for longer-lasting and non-staining products. The relatively low molecular weight (MW) antioxidants have undergone an evolutionary change towards higher molecular weight products with the objective to achieve permanence in the rubber polymer, without loss of antioxidant activity. In the last two decades, several approaches have been evaluated in order to achieve this objective: attachment of hydrocarbon chains to conventional antioxidants in order to increase the MW and compatibility with the rubber matrix; oligomeric or polymeric antioxidants; and polymer bound or covulcanizable antioxidants. The disadvantage of polymer bound antioxidants was tackled by grafting antioxidants onto low MW polysiloxanes, which are compatible with many polymers. New developments on antiozonants have focused on non-staining and slow migrating products, which last longer in rubber compounds. Several new types of non-staining antiozonants have been developed, but none of them appeared to be as efficient as the chemically substituted p-phenylenediamines. The most prevalent approach to achieve non-staining ozone protection of rubber compounds is to use an inherently ozone-resistant, saturated backbone polymer in blends with a diene rubber. The disadvantage of this approach however, is the complicated mixing procedure needed to ensure that the required small polymer domain size is obtained

Alkylated phenolic resins as antioxidants for rubber

Polymeric antioxidants based on p-nonyl phenol formaldehyde resin (PNPF) and p-dodecyl phenol formaldehyde resin (PDPF) were prepared by the condensation reaction of the respective phenols with formaldehyde in the presence of an acid catalyst. The reactions were monitored by thin layer chromatography, and the melting points of the products were determined. These compounds were incorporated in natural rubber mixes to evaluate their antioxidant properties. The compounded mixes were characterized for their rheometric properties. The compression-molded rubber sheets were tested for their mechanical properties. The effects of aging on the mechanical properties of these molded sheets were evaluated. Both PNPF and PDPF showed better antioxidant properties than the conventional styreneated phenol antioxidant. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2649–2651, 2006

Effect of Some Polymeric Phenolic Antioxidants on the Properties of SBR Vulcanizates

ABSTRACT Polymeric antioxidants can be useful in the protection of styrene-butadiene rubber (SBR) against thermal oxidative aging as an alternative to the low molecular weight ones, which migrate out of the rubber articles. Three polymeric compounds were prepared and incorporated into SBR mixes to be evaluated as antioxidants in comparison with the commercial antioxidant, N-isopropyl-N′-phenyl-p-phenylenediamine (IPPD). The rheometric characteristics of the produced SBR mixes were measured and the cure time was determined. The mechanical, swelling, extraction, and compression properties were studied. The results obtained revealed that poly(4-mercaptophenyl)acrylamide has superior effect in the protection of SBR articles against thermal oxidative ageing.

Alkylated phenolic antioxidants for paints

Polymeric antioxidants based on p-cumyl phenol formaldehyde resin (PCPF), p-nonyl phenol formaldehyde (PNPF) and p-octyl phenol formaldehyde (POPF) were prepared by condensation reaction of respective phenols with formaldehyde in presence of an acid catalyst. The reactions were monitored by TLC and the melting point of the products was determined by open capillary method. Stabilising the action of PCPF, PNPF for protecting paint against thermal oxidation was tested using a QUV weatherometer. The effect of exposure on the properties of paints such as gloss, whiteness and yellowness were evaluated. Results show that paints containing these new polymeric antioxidants possess better stabilising effects against photo-oxidation than those employed in standard paints available in the market.

Addressing Durability of Rubber Compounds

Abstract The developments on long-term protection of rubber against aerobic aging are reviewed. Although conventional antidegradants such as N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD) and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) are still the most widely used antidegradants in rubber, there is a trend and demand for longer-lasting and non-staining products. The relatively low molecular weight (MW) antioxidants have undergone an evolutionary change towards higher molecular weight products with the objective to achieve permanence in the rubber polymer, without loss of antioxidant activity. In the last two decades, several approaches have been evaluated in order to achieve this objective: attachment of hydrocarbon chains to conventional antioxidants in order to increase the MW and compatibility with the rubber matrix; oligomeric or polymeric antioxidants; and polymer bound or covulcanizable antioxidants. The disadvantage of polymer bound antioxidants was tackled by grafting antioxidants on low MW polysiloxanes, which are compatible with many polymers. New developments on antiozonants have focused on non-staining and slow migrating products, which last longer in rubber compounds. Several new types of non-staining antiozonants have been developed, but none of them appeared to be as efficient as the chemically substituted p-phenylenediamines. The most prevalent approach to achieve non-staining ozone protection of rubber compounds is to use an inherently ozone-resistant, saturated backbone polymer in blends with a diene rubber. The disadvantage of this approach, however, is the complicated mixing procedure needed to ensure that the required small polymer domain size is achieved.

Synthesis and performance of phenolic polybutadiene‐bound stabilizers

AbstractAn antioxidant derivative, 6‐sulfanylhexyl 3‐(3,5‐di‐tert‐butyl‐4‐hydroxyphenyl)propanoate, was synthesized and examined. With a radical initiator, the addition of this compound to pending vinyls of OH‐telechelic, low molecular weight liquid polybutadiene (LBH) was performed to various degrees of conversion to form polymeric antioxidants (PAOs) in which the phenolic moiety was separated from the main chain by a spacer [CH2CH2S (CH2)6OCO]. Pure, unstabilized LBH was mixed in several ratios with PAOs, Irganox 1520, and Irganox 1076, and the oxidation stabilities of these mixtures, determined by thermogravimetric analysis and differential scanning calorimetry, were compared. Probably because of their good compatibility with LBH, PAOs exhibited equal or better effectiveness than commercial antioxidants of the Irganox type. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 885–889, 2003

Polymeric Antioxidants. V. Ortho Methylene-bridged and Direct-linked Sesamol Oligomers

Two types of sesamol oligomers, ortho methylene-bridged and direct-linked oligomers, were prepared and their antioxidant effects on the autoxidation of lard and tetralin were evaluated. The methylene-bridged oligomers were prepared by the reaction of sesamol, a major antioxidative compound in sesame seed, with ethylmagnesium bromide and subsequent oligomerization with paraformaldehyde. During the reaction, methylidenedioxy moieties of the sesamol oligomers were partially cleaved and the addition of hydroxyl groups was observed. The methylene-bridged oligomers had much stronger antioxidant effects on the autoxidation of lard than the sesamol monomer. And the oligomers, having a larger average number of hydroxyl groups per sesamol unit, were a more efficient antioxidant for lard. Direct-linked oligomers were synthesized by an oxidative coupling of sesamol by hydrogen peroxide using horseradish peroxidase as a catalyst. Molecular structures of the direct-linked oligomers were influenced by the pH of the buffer solution in which the oxidations were carried out. Oligomers having a larger number of hydroxyl groups were prepared under more acidic conditions. The direct-linked oligomers prepared in acidic conditions were better antioxidants of lard than the sesamol, whereas oligomers prepared under neutral and alkaline conditions did not improve the antioxidant effect. Both methylene-bridged and direct-linked oligomers inhibited the autoxidation of tetralin; but, in contrast to the lard results, almost all of the oligomers were less effective antioxidants for tetralin than the sesamol monomer.

Polymeric Antioxidants from Vernonia Oil

The antioxidative activity of the title stabilizers has been studied by the initiated oxidation of cumene as a model reaction. The new model compounds prepared from vernonia oil and the conventional phenolic antioxidant 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (DTBH) and, copolymerized with styrene, showed that the rate constant of inhibition, k7, weakly depends on the size and the nature of the radical, R∗, whose magnitude was found to be k7 = 107.0±0.5 exp(4 200 ± 700)/RT L/mol·s. The antioxidative activities of the new compounds compare favorably with the commercial product used in technology. These phenolated vernonia oil derivatives were incorporated chemically to polystyrene and polyurethanes, forming polymeric antioxidants useful for master batches for the named polymeric materials.

Synthesis and characterization of polymeric antioxidants based on oligo(styrene- co-chloromethyl styrene)

Oligo (styrene- co-chloromethyl styrene) with a molecular weight range of between 1 × 10 3 and 4 × 10 3 g mol -1 reacts with potassium 2, 6-di-tert-butylphenoxide salt in dimethyl formamide (DMF) to form polymeric antioxidants. The functionality of such antioxidants was determined by titrating the residual chlorine. When an ammonium salt, such as t−Bu 4N +Br -, was added to the reaction medium as a catalyst, the efficiency of functionalization could be improved to up to 96%. The functionality of the polymeric antioxidants increases with a decrease in the ratio of styrene to chloromethyl styrene. Instead of DMF, dioxane/water ( 20 1 v v ) as the reaction solvent can also give a high yield of functionalization.

Hydrogen bonded polymer blends and the design of miscible polymeric antioxidants

AbstractThe relative magnitude of the equilibrium constants describing self‐association versus inter‐association is an important factor in determining the phase behavior of polymers that hydrogen bond. In studies of sterically hindered phenolics we have found that poly(2,6‐diisopropyl‐4‐vinylphenol) (PDIPP) only moderately self‐associates, but strongly inter‐associates with polymers containing groups such as ester carbonyls, ether oxygens, and the like. PDIPP is miscible with polytetrahydrofuran (PTHF) and simultaneously acts as an efficient polymeric antioxidant. This result points the way to the design of specific miscible polymeric antioxidants for polar polymers.

Synthesis and test of styrene?Cyclosiloxane and butadiene-cyclosiloxane block copolymers containing ultraviolet (UV) absorber and antioxidant groups

Block copolymers of polystyrene and poly(dimethylsiloxane) or of polybutadiene and poly(dimethylsiloxane) with nonhydrolyzably bound 2-hydroxybenzophenone and 2,6-di-tert-butylphenol residues were prepared by terminating the “living” block copolymers with glacial acetic acid to form siloxanol end groups, followed by condensation with diethoxysilyl derivatives of the stabilizers in the presence of dibutyltin dilaurate. The polymeric UV absorbers were proved to be nonextractable from polystyrene. At Xenotest aging (40°C) the polymeric UV absorbers were less effective than 2-hydroxy-4-octyloxybenzophenone. The polymeric antioxidants were superior to antioxidants of low molecular weight both in thermooxidative aging of vulcanized polybutadiene films at 70°C and in oxygen-uptake studies with stabilized polypropylene at 180°C over long periods.

Polymerization products of p-benzoquinone as bound antioxidants for SBR. Part II—The antioxidizing efficiency

The antioxidizing efficiency of the polymeric products of p-benzoquinone as bound antioxidants for SBR has been investigated by measuring the percentage deterioration of tensile strength and ultimate elongation for the thermally aged rubber samples after up to 14 days in an air oven at 100°C. The results indicate the remarkable antioxidizing efficiency of these products for SBR compared with the common industrial antioxidants. The higher efficiency is attributed to the ability of the polymeric antioxidants to react with the radical intermediates of the oxidative degradation process, thus bonding them chemically to the rubber chains. The effect of the polymeric antioxidants on the rate of sulfur vulcanization has also been studied. The results reveal that, depending on the quinone/hydroquinone ratio of the product, the polymeric antioxidants may accelerate or slightly retard the rate of vulcanization. The results also indicate that blending the polymeric quinones in equal proportions with an amine antioxidant 6PPD leads to a pronounced improvement in the antioxidizing efficiency of the resulting stabilizer without affecting the rheological or other properties of the rubber. A mechanism for the antioxidant action is proposed.

Functional Polymers. XLIII. Olefin Copolymers of 2, 6-Di-t-butyl-4-vinyl (or 4-isopropenyl) phenol

Abstract Several new polymeric antioxidants have been synthesized based on 2,6-di-t-butyl-4-vinyl (or isopropenyl) phenol. They were prepared by emulsion copolymerization with 1,3-butadiene or isoprene and had about 6 to 10 mol% of the polymerizable hindered vinyl (or isopropenyl) phenol in the copolymers. The copolymers were catalytically hydrogenated in the presence of soluble cobalt catalysts to saturated copolymers of ethylene or ethylene/propylene structure. The polymers are apparently not branched and had molecular weights up to 50 000.

Vitamin E deficiency in rabbits receiving a high PUFA diet with and without a non-absorbable antioxidant. II. Incorporation of 14C-labelled glycine and L-leucine into liver and plasma proteins.

As determined by in vivo studies using [1-14C] L-leucine and [1-14C] glycine, vitamin E deficiency in young rabbits caused a higher turnover rate of liver proteins and of plasma albumin and globulin fractions. This effect was most clearly and consistently observed in animals fed a diet containing 10 mg of the non-absorbable polymeric antioxidant Anoxomer per g of fat in the diet.

Retardation of rancidity in deep‐fried instant noodles (ramyon)

AbstractThe storage stability of instant fried noodles (ramyon) was determined by accelerated aging at 63 C with organoleptic evaluation of the onset of rancidity. Three methods of extending the shelf‐life of ramyon were examined: (a) addition of 200 ppm antioxidant, butylated hydroxyanisole (BHA), t‐butylhydroquinone (TBHQ), or a polymeric antioxidant (Poly‐A) to the frying (palm) oil; (b) coating the inner surface of the polyethylene package with TBHQ equivalent to 200, 500 and 1000 ppm based on the oil in the ramyon; and (c) addition of a mixture of 200 ppm TBHQ and 200 or 500 ppm disodium ethylene‐diaminetetraacetate (EDTA) to the frying oil. When the antioxidants were added to the oil, BHA and Poly‐A approximately doubled while TBHQ tripled the shelf‐life of ramyon. The mixture of TBHQ (200 ppm) and disodium EDTA (500 ppm) in the frying oil quintupled the shelf‐life. The inner surface application of TBHQ (200 ppm) extended shelf‐life twice that of an equal amount of TBHQ in the frying oil. Rancid off‐flavors developed slowest in noodles with aw 0.3. Hexanal concentration in ramyon was a good indicator of the development of oxidative rancidity. Organoleptic evaluation showed the flavor of ramyon was objectionable when hexanal concentration reached 3.5 ppm based on the weight of ramyon (as is). The relative effectiveness of antioxidants in preventing off‐flavor in ramyon could be determined from the hexanal concentration in stored ramyon.