A new antagonism between hindered amine light stabilizers and acidic compounds including phenolic antioxidant

2007

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The interaction between hindered amine light stabilizers (HALS), and ultraviolet absorbers (UVA) was investigated, in order to clarify the reason why they generally show synergism, although UVA belong to kinds of phenols. A homolytic decomposition of cumene hydroperoxide (CHP) by amine-type HALS (HALS NH) in the presence of UVA is the antagonism bringing about autoxidation. This antagonism is found considerably weaker for UVA than that of 3,5-di-t-butyl-4-hydroxytoluene. This is based on a weak proton-donating ability of UVA to HALS due to their intramolecular hydrogen bond. Furthermore, a good relationship was found between the inhibition of photo-oxidation by UVA and the initial rate of homolytic decomposition of CHP by HALS in the presence of UVA, and a strong synergism of UVA with HALS was observed. As a result, UVA are able to exhibit an apparent synergism in a combination with HALS, because of no or little acceleration (antagonism) of homolytic hydroperoxide decomposition caused by the interaction with HALS, as well as the estimated regeneration (synergism) of new UVA from the corresponding quinoide-type compounds, even if formed, by the action of HALS or the derivatives.

Section: I N F L U E N C E O F U Va -1 a N D L I G H T O Nsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Influence of Ultraviolet Absorbers on Decomposition of Hydroperoxide by Hindered Amine Light Stabilizers

Mizokawa

2007

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“…We propose a formation mechanism for the active species, HALS nitrosonium salt, on the basis of abovementioned results and our previous results 1) . In general, a less basic HALS has lower antagonism with a phenol, as explained by step (1) of Scheme 2.…”

Section: Formation Mechanism Of Active Speciesmentioning

confidence: 57%

“…However, the mechanism of antagonism generally accepted at present does not describe all of observed antagonisms. We have previously proposed a new antagonism 1) . Hydroperoxide decomposition by HALS is a very important process, and consists of two phases: slow decomposition in the induction period, and fast decomposition which proceeds homolytically.…”

Section: Introductionmentioning

confidence: 99%

New Antagonism of Hindered Amine Light Stabilizers with Acidic Compounds Including Phenolic Antioxidants (Part 2) Formation Mechanism of Active Species of Peroxide Decomposition Reaction

Yamashita

Kawaguchi

2006

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The effect of acidic compound on the formation of active species in homolytic hydroperoxide decomposition by hindered amine light stabilizers (HALS) was studied. The hydroperoxide decomposition activity of HALS is an important to characteristics of HALS. HALS Ammonium salt, which is a fundamental compound involved in the antagonism between HALS and acidic compounds including phenolic antioxidants, was found to be a key compound for the formation of HALS nitrosonium salt, which was identifi ed as the active species of hydroperoxide decomposition. HALS Nitrosonium salt was not formed from active species for polymer stabilization, such as nitroxide, alkoxide, or hydroxylamine of HALS, but from HALS salt. A formation mechanism of HALS nitrosonium salt is proposed. Furthermore, molecular aggregates formed between HALS and acid compounds are discussed to be important for HALS properties.

“…In particular, a hydroperoxide decomposition by HALS is an important step forming active species of HALS for stabilization. In a previous paper, the authors reported a new fact that a hydroperoxide decomposition by HALS NH proceeds through homolytical chain reactions and is accelerated by the presence of 3,5-di-t-butyl-4-hydroxytoluene (BHT), one of phenolic antioxidants 1) . In addition, they also reported that a nitrosonium salt of HALS is produced during a hydroperoxide decomposition by HALS, and its formation is accelerated by a phenol.…”

Section: Introductionmentioning

confidence: 99%

Interaction of Hindered Amine Light Stabilizers and Ultraviolet Absorbers

Takenaka

Mizokawa

2007

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The reason is discussed, why ultraviolet absorbers (UVA) having phenolic moiety show the synergism with HALS apparently, on the contrarily to phenolic antioxidants. A HALS nitrosonium is a substrate causing the useless oxidation of a phenol, and is formed from HALS more easily in the presence of a phenol. However, 2-hydroxybenzophenone (2-HBP) did not accelerate the formation of the nitrosonium so fast as 3,5-di-t-butyl-4-hydroxytoluene (BHT). A HALS nitrosonium, even if formed, did not oxidize 2-HBP so much as BHT. That is, 2-HBP can continue to work longer and more effi ciently in the presence of HALS. This fact suggests a weak antagonism of 2-HBP and a strong antagonism of BHT with HALS. On the other hand, quinones, derived from 2-HBP and BHT as result of peroxy radical-catching, were reduced to the corresponding hydroquinones by the action of HALS derivatives, such as HALS hydroxylamine. This reaction occurs strikingly faster and more easily for 2-HBP than for BHT. This fact shows a strong synergism of 2-HBP and a weak synergism of BHT with HALS. The above-mentioned results well explain the apparent synergism of UVA (2-HBP) with HALS, contrarily to the apparent antagonism of BHT with HALS.