Polymer Degradation and Stability
Volume 74, Issue 1,
2001
, Pages 189-193
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Abstract
The antioxidant activity of hydroxychromanones and hydroxychromanes with a thiopropionate group in the oxidation of tetralin was evaluated at 61 and 140°C. Both phenols were found to be intrinsically much more active at high temperature than the corresponding forms without a thiopropionate group. This high activity is attributed to an additional antioxidant function resulting from the introduction of a thiopropionate group into the aromatic ring.
Introduction
All organic materials exposed to air undergo oxidative degradation. Therefore, the inhibition of oxidation by molecular oxygen is important in polyolefins during processing and fabrication, as well as for long-term stability when the fabricated polymer product is subjected to various environmental conditions. Furthermore, oxidation is the main cause of deterioration of rubber products and lubricating oils. Consequently, the inhibition of these oxidations has attracted much attention and various natural and synthetic antioxidants are now on the market. For example, α-tocopherol (α-Toc) and 2,6-di-tert-butyl-4-methylphenol (BMP, often called BHT) are popular as natural and synthetic antioxidants, respectively. However, in polymer stabilization technology, the combination of antioxidants with other stabilizers is well known to produce a synergistic stabilizing effect. For example, hindered amine light stabilizers were shown to have a synergistic effect in combination with aliphatic phosphites under photo-oxidative conditions [1]. Synergistic stabilizing effects and molecular interactions between hindered phenols and aromatic phosphites during polymer processing are also reported [2], [3]. For mixtures of the half-hindered phenolic antioxidant 3,9-bis(2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy)-1, 1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5] undecane (Sumilizer GA-80) [4] with 3,3′-thiodipropionate-type antioxidants, intermolecular cooperation among various combinations in the stabilization of polypropylene has been reported and mechanisms proposed [5]. In the case of the fully-hindered phenol, pentaerythrityl tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (Sumilizer BP-101), the synergistic stabilizing effect was inferior to that of GA-80, particularly in combination with pentaerythrityl tetrakis(3-laurylthiopropionate). The half-hindered phenol, GA-80, can associate with the ester groups of the dilauryl 3,3′-thiodipropionate, and these two antioxidants would be close to one another. Thus, the hydroperoxide produced by the reaction of peroxyl radical with GA-80 will react smoothly with thiopropionate, and the synergistic effect will be enhanced.
Scott et al. [6], [7] have reported that a series of alkyl(3,5-di-tert-butyl-4-hydroxybenzyl) sulphides (BHBS) containing sulphidically bound sulphur in their molecule were more effective than an equimolar mixture of a simple hindered phenol (BHT) with the same antioxidant functional group and a non-phenolic sulphide (BS). This effect was due to the peroxide decomposing activity of the sulphur moiety. Indeed, this type of phenolic antioxidant (Irganox 1520) has been commercialized by Ciba SC.
Previously, we reported that hydroxychromanones, which have a fused heterocyclic ring, exhibit excellent antioxidant activities [8]. On this basis, we expected the introduction of a thiopropionate group into the benzene ring of hydroxychromanone or hydroxychromane to result in good antioxidant activity with intramolecular stabilizing effects.
Section snippets
General
Melting point (mp) data were measured with Yanaco MP-J3 micro-melting apparatus and are uncorrected. Nuclear magnetic resonance spectra were recorded with a Jeol GSX-400 spectrometer operated at 400 MHz for 1H and at 100.6 MHz for 13C in CDCl3, and chemical shift data are with reference to (CH3)4Si.
Assay for antioxidant activity
The rate of oxygen absorption was measured as a function of time under 760 Torr (1 Torr=133.3 Pa) of O2 with 50.0 g of tetralin containing an antioxidant (1.03 mM) and α,α′-azobisisobutyronitrile
Inhibition of oxidation of tetralin by phenols initiated by AIBN at 61°C
Fig.2 shows examples of oxygen-uptake curves for the oxidation of tetralin initiated by AIBN at 61°C. In the absence of an antioxidant (control), the oxidation proceeded with a very brief initiation period at a constant rate of oxygen uptake. In the presence of 1–6 and α-Toc, the rate of oxygen uptake was significantly suppressed and a distinct induction period (tinh) was observed. When the induction period was over, the oxidation proceeded at the same rate as that in the absence of a radical
Acknowledgements
This work was partially supported by the Kansai University Grant-in-Aid for the Faculty Joint Research Program, 2001.
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Cited by (7)
Structure effect of benzofuranone on the antioxidant activity in polypropylene
2010, Polymer Degradation and Stability
Citation Excerpt :
In addition to this, the substituent having double bond or unpaired electrons such as alkoxy allows strong electron delocalization [16]. As a result, when the substituents having strong electron donating ability are incorporated in antioxidant molecules, the antioxidant activity will be improved obviously [13,17–19]. Thus, in this work, the ANBF1 and ANBF2 (The structures were shown in Scheme 1), which contain stronger electron donating substituent —4′-position methoxyl group— compared to methyl group, were designed, and the antioxidant activity in PP were compared with TBF1 and TBF2 having 4′-position methyl group using MFI values and FT-IR of PP stabilized by those benzofuranone compounds.
This work deals with the antioxidant activity of benzofuranone compounds in polypropylene (PP). The antioxidant activities of ten benzofuranone compounds in PP were compared using melt flow index (MFI) values of PP stabilized by benzofuranone compounds primarily. The results show: firstly, that the increase of electron donating ability of substituent in 3-substituted benzene ring is beneficial to the improvement of antioxidant activity. Secondly, it has been verified that the steric hindrance of 2′-position substituent can weaken the antioxidant activity of benzofuranone. But when 2′-position substituent forms a hydrogen bond with 3-position reactive hydrogen, the steric hindrance is offset efficiently. Finally, the methyl and tert-butyl groups in the 5 and 7-position of parent benzene ring do not affect the antioxidant activity of benzofuranone compounds in PP obviously.
New bifunctional antioxidants - Intramolecular synergistic effects between chromanol and thiopropionate groups
2003, Polymer Degradation and Stability
Citation Excerpt :
Another example of the synergistic stabilizing effect is a combination of trivalent organo-phosphorus compounds with hindered phenols or hindered amine light stabilizers with phenolic antioxidants [2,3]. In a previous paper [4], we reported that hydroxychromanones and hydroxychromanes with a thiopropionate group in the same molecule act as potent antioxidants at high temperature. During the course of this work, we found that 3-(6-hydroxy-2,2,5,7-tetramethyl-chroman-8-ylsulfanyl)-propionic acid ethyl ester exhibits a long induction period at high temperature.
We have examined the antioxidant activities, both in tetralin oxidation induced by an azo initiator and in tetralin under thermoxidative conditions of a series of tetramethyl-6-chromanols with a methyl thiomethyl, phenyl thiomethyl, methyl thiopropionate, and thiopropionate group. The antioxidants tested showed almost the same activity for the oxidation of tetralin induced by an azo initiator at 61°C. At high temperature, we found that tetramethyl-6-chromanols with a thiopropionate group increased the induction period for ortho to the OH group by 7.5-fold and meta to the OH group by 10.7-fold, compared with that for pentamethyl-6-chromanol.
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