- Email: [email protected]
A review on the mechanism of action and applicability of Hindered Amine Stabilizers
Accepted Manuscript A review on the mechanism of action and applicability of Hindered Amine Stabilizers Pieter Gijsman PII:
S0141-3910(17)30135-0
DOI:
10.1016/j.polymdegradstab.2017.05.012
Reference:
PDST 8231
To appear in:
Polymer Degradation and Stability
Received Date: 20 March 2017 Revised Date:
4 May 2017
Accepted Date: 17 May 2017
Please cite this article as: Gijsman P, A review on the mechanism of action and applicability of Hindered Amine Stabilizers, Polymer Degradation and Stability (2017), doi: 10.1016/ j.polymdegradstab.2017.05.012. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
A review on the mechanism of action and applicability of Hindered Amine Stabilizers
RI PT
Pieter Gijsman
DSM Ahead b.v., P.O. Box 18, 6160 MD Geleen, The Netherlands Tel.: 0031 46 4761538. E-mail address: [email protected]
1
SC
Key words: UV-stability, long-term heat stability, antagonism, synergisms, HALS, HAS
Abstract
M AN U
Hindered Amine Stabilizers (HAS) are by far the best performing UV-stabilizers and in a number of applications they are the best performing long-term heat stabilizer too. In this paper an overview is given of the different mechanisms proposed that can explain the high activity as well as the applicability of HAS as UV-stabilizer and as long-term heat stabilizer.
2
Introduction
TE D
After the introduction of the first hindered amine light stabilizer (HALS) in the 1970ths, they rapidly became the most important UV-stabilizer for the majority of plastics. Due to their high activity they are nowadays in use for the light stabilization of many organic polymers (e.g. polyethylene, polypropylene, thermoplastic polyolefins and elastomers,
EP
coatings, styrenic polymers, polyamides, polyurethanes, polyacetals adhesives and sealants). Without the discovery of HALS the outdoor applicability of many polymers
3.
AC C
would be limited. The good performance of HAS is clearly shown in references 1, 2 and
The invention of HALS was based on the discovery that the 2,2,6,6-tetramethyl-1piperidinyloxy free radical ((TEMPO) Fig. 1) is a very effective radical scavenger [4,5]. However, due to its physical and chemical properties TEMPO itself cannot be applied. TEMPO is coloured, and thus will discolour a polymer, it is thermally unstable and volatile [5]. It can also react with phenolic antioxidants present in many polymers as processing and/or long-term heat stabilizer. The discovery that compounds in which the N-oxyl functionality was replaced by a N-H functionality also showed good UV
ACCEPTED MANUSCRIPT
stabilization activity was the key finding that led to the development of HALS stabilizers [5].
O Fig. 1. Chemical structure TEMPO
RI PT
N
SC
Although HALS stabilizers were developed as UV-stabilizer, it is more and more
recognized that these molecules could also impart long-term heat stability. Especially when phenolic antioxidants cannot be used due to secondary reasons as e.g.
M AN U
discolouration, HALS is used to protect polymers against long-term heat degradation [6]. Consequently the in use abbreviation was changed from HALS (Hindered Amine Light Stabilizer) into HAS (Hindered Amine Stabilizer).
Nowadays there are many HAS stabilizers commercial of which the majority are based on 2,2,6,6-tetra-methyl-4-piperidinyl derivatives. An overview of the chemical structures as well as a non-comprehensive list of brand names and suppliers of the HAS and the
TE D
other stabilizers mentioned in this paper is given in Appendix 1. The first commercial HAS (HAS-1) is relatively low in molecular weight, which means that due to its high volatility it is not suitable for thin applications. To overcome this problem oligomeric HAS types (as e.g. HAS-2) were developed. One of the drawbacks of the piperidinyl moiety of HAS stabilizers is that it is basic, which means that it can react with acids and forms a
EP
not stabilizing salt. Consequently, the effectiveness of HAS in systems where acids are present or can be formed is limited. To beat this problem less basic HAS stabilizers as
AC C
e.g. N-O-R types were developed, a commercial example is HAS-3. Since the discovery of HAS, a lot of research was done on their mechanism of action and many different mechanisms were proposed. At the moment, there is still no consensus, which might be related to the fact that the mechanism of action of HAS is circumstances dependant. So are results of the mechanism of action in different polymers, from UV-degradation with different light sources and even from thermooxidative degradation compared. In the following an overview of the proposed mechanisms of action and the applicability of HAS is given.
ACCEPTED MANUSCRIPT
3
Mechanism of action of HAS Since the discovery of HAS stabilizers, a lot of research was done on their
mechanism of action and many different mechanisms were proposed. ESR studies on the stabilizing activity of HAS showed that the piperidinyl moiety
RI PT
(amine) is easily converted in a piperidinoxyl radical (nitroxide) [7,8,9,10]. Together with the knowledge that these radicals are stable and excellent alkyl radical scavengers, it was easily concluded that they play an important role in their stabilizing activity. Shilov et al. [11] detected the consumption of nitroxide during the cumyl
hydroperoxide initiated degradation of PP in an argon atmosphere, whereas in this
SC
experiment the addition of oxygen led to an increase of the nitroxide concentration. From this it was concluded that the nitroxide can be regenerated, which could explain the high
M AN U
effectiveness of HAS. After this discovery a lot of research was done on the mechanism of action of HAS and several mechanism were proposed. The majority of these mechanisms are based on radical scavenging in which the formation of the nitroxide as well as its regeneration plays a key role. In the following an overview of the proposed nitroxide formation and regeneration mechanisms as well as other possible HAS
3.1
TE D
stabilization mechanisms is given.
Nitroxide formation mechanisms
For the conversion of HAS to the corresponding nitroxide several mechanism were proposed. In the majority of these mechanisms the amine is oxidized by polymer
EP
oxidation products, which is in agreement with the observation that the stabilization effect of HAS only start after some accumulation of hydroperoxides [12,13]. For this
AC C
conversion the absence of α-hydrogens in the amine is essential, as otherwise the amine is converted into a nitrone [14]. Thus, although these stabilizers are called Hindered Amines, the function of the 4 methylene groups is not introducing steric hindrance, but eliminating α-hydrogens. It was postulated that the nitroxide is formed by a reaction of a hydroperoxide
with the amine followed by the reaction of the formed alkoxyamine with a peroxy radical [13]. Alternatively a hydroxyl amine is formed that is transformed into the nitroxide (Scheme 1), which of these two reactions is preferred depend on the polymer type [15].
ACCEPTED MANUSCRIPT
N - H2O
+ ROOH N
O
or
+ ROO - ROOR
R + ROO
- ROH
N O
RI PT
- ROOH
H N OH
Scheme 1. Possible reactions of a hindered amine to a hydroxyl or
SC
alkyloxyamine
Alternatively the nitroxide is formed from the reaction of the amine with a peroxy
M AN U
radical leading to an aminyl radical that in a sequence of oxidation reactions is transferred into a nitroxide (Scheme 2) [16].
O N
2
O / H R
N
H 2 O R +
2
O R + H N
Scheme 2. Reaction of a hindered amine with a peroxy radical leading to a
TE D
nitroxide [16].
EP
H O R +
2
O R + H N
O N
It was also suggested that the nitroxide directly can be formed from the reaction of a hindered amine with a peroxy radical, which lead to a nitroxide and an alcohol (Scheme 3 [17]).
AC C
Scheme 3. Formation of a nitroxide from the reaction between a hindered amine and a peroxy radical [17].
It was also proposed that the formation of the nitroxide can be a result of a reaction of the amine with oxidation products that are formed. Toda et al. [18] assumed that the nitroxide is formed by a reaction of a peracid with the hindered amine (Scheme 4) and Felder [19] suggested a reaction between an acylperoxy radical and the hindered amine to form the nitroxide and an acid (Scheme 5).
ACCEPTED MANUSCRIPT
Zahradnickova et al. [20] showed that the nitroxide indeed can be formed by the reaction of the amine with oxidized polypropylene (PP) containing peracids.
RI PT
O 2 H + O N
2 + H O
O C
R 3
H O
O
O C
R 3 + H N
2
Scheme 4. Formation of the nitroxide according to Toda et al .[18].
M AN U
SC
O N
+ H O
O C
R
O
O
O C
R + H N
Scheme 5. Formation of the nitroxide according to Felder [19]
More recently it was suggested that the nitroxide can be formed from its charge
EP
TE D
transfer complex with oxygen (Scheme 6 [21]).
Scheme 6. Formation of the nitroxide from the excited charge transfer complex of
AC C
the amine with oxygen [21]
The majority of the commercially available hindered amine stabilizers are secondary amines, however in some cases tertiary amines (>N-CH3) are used (e.g. HAS-4). The transformation of the tertiary amine to the nitroxide is more complicated. The most logical explanation is that the tertiary amine is first oxidized to a secondary amine, from which the nitroxide is formed [12]. This mechanism was confirmed with high-level ab initio molecular orbital theory calculations [22].
ACCEPTED MANUSCRIPT
3.2
Nitroxide regeneration mechanisms
The high activity of hindered amine stabilizers was ascribed to the possibility that the formed nitroxide can be regenerated in a cyclic reaction [11]. The mechanism causing this regeneration is still under debate and many variations are proposed. Shilov and
RI PT
Denisov [23] proposed that the nitroxide is regenerated in a reaction between the
M AN U
SC
aminoether and a peroxy radical, this reaction is called the ‘Denisov cycle’ (Scheme 7).
Scheme 7. Nitroxide regeneration mechanism according to the Denisov cycle.
There are many variations on the Denisov cycle suggested, but all of them are based on
TE D
the regeneration of the nitroxide. According to Bolsman [24] the cyclic mechanism that is responsible for the catalytic scavenging of tertiary alkyl and peroxy radicals involves the
AC C
EP
formation of a hydroxylamine from the alkyloxyamine (Scheme 8).
Scheme 8. Nitroxide regeneration involving the formation of a hydroxyl amine [24]
ACCEPTED MANUSCRIPT
It was shown that HAS stabilizers are effective in model systems that can form peracids [25,26], it was also shown that peracids play an important role in the thermo-oxidative degradation of PP [6]. According to Step et al. [27,28] peracyl radical plays a key role in
M AN U
SC
RI PT
the nitroxide regeneration mechanism (Scheme 9).
TE D
Scheme 9. Nitroxide regeneration involving peracyl radicals [27,28].
Using high-level ab initio molecular orbital theory calculations of the free energy barriers and reaction energies in the gas phase and in solution, a comparison between the
EP
different postulated mechanisms was made [22]. Based on this calculations it was concluded that the nitroxide regeneration reaction depends on the absence or presence of β-or γ-hydrogen atoms in the alkoxy amine (Scheme 10). However, for the reaction
AC C
rate, besides the reaction constant, the concentration of reagents is important too, some of the concentrations of species mentioned in this mechanism are expected to be that low that these reactions does not seem very likely.
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Scheme 10. Nitroxide regeneration mechanism for alkoxyamines with a β- (top) or γ-
TE D
(bottom) hydrogen atom [22]
In all the nitroxide regeneration mechanisms shown above the nitroxide reacts with an alkyl radical, this reaction is in competition with the extremely fast reaction between an alkyl radical and oxygen (kO2) (Scheme 11). The reaction rate between the nitroxide and
EP
an alkyl radical (kNO) was investigated by several groups. It was shown that kNO/ kO2 is
AC C
about 0.1 to 0.25 [29,30,31,32].
Scheme 11. Competition reactions between an alkyl radical and oxygen or a nitroxide radical
ACCEPTED MANUSCRIPT
For the relative reaction rates, the ratio between the concentrations of oxygen and nitroxide is important too. For polyolefins, it was shown that the concentration of the nitroxide is an order of magnitude smaller than that of oxygen, which means that only
RI PT
about 1-2.5% of the alkyl radicals reacts with the nitroxide instead of reacting with oxygen. Consequently the kinetic chain length (amount of times an alkyl radical will
propagate before it terminates) becomes 40-100, which still is small in comparison to the for free radicals in PP published value of 1.75 104 [33]. This shows that even when the
concentration of the nitroxide is limited, it still can reduce the kinetic chain length largely.
SC
Above consideration assumes a homogenous distribution of the nitroxide, however it is shown that degradation is a heterogeneous process [34,35,36,37,38,39]. If the HAS or
M AN U
its nitroxide concentrate in these oxidizing areas, their concentration increases causing an increased alkyl radical scavenging rate. A possibilities for an increased concentration in the oxidizing zones is the formation of associates between hydroperoxides and HAS. Associates between amines and hydroperoxide were reported [13,40]. In model experiments Grattan et al. [41] found for zones being equimolar in hydroperoxide and alkane segments a 26 fold increase in the concentration of nitroxide radicals. From this result it was suggested that association through hydrogen bonding, between the
TE D
nitroxide and hydroperoxides, causing an increase of the local nitroxide concentration to a level at which the reaction of the nitroxide with an alkyl radical could successfully compete with the reaction of an alkyl radical with oxygen. Another possibility for the increased concentration of nitroxides in oxidized zones is the
3.3
EP
formation of charge transfer complexes between peroxy radicals and HAS [42].
Other possible stabilization mechanisms
AC C
Besides the above mentioned radical scavenging activity of HAS a number of potential additional stabilizing roles of HAS are published. These roles are described below.
3.3.1 Transition metal complexation. It is well known that transition metals can initiate the photo-oxidation of polymers, by catalysing the hydroperoxide decomposition [43]. Fairgrieve and McCallum [44,45] showed that HAS is capable in complexing transition metals. This complexation can cause a decrease in the decomposition rate of hydroperoxides into initiating radicals.
ACCEPTED MANUSCRIPT
Moreover, due to complexation of initiating transition metals an increased concentration of HAS in the oxidizing zones can be expected.
RI PT
3.3.2 Hydroperoxide decomposition In Scheme 1 the decomposition of a hydroperoxide by a HAS is depicted, this reaction
can lead to an increase in stability too. However, it is shown that piperidinyl derivatives have hardly any influence on the photolysis rate of t-butylhydroperoxide in an inert
environment [25,46], nor on the decomposition of cumyl hydroperoxide at 120°C in
SC
chlorobenzene [25]. From these results, it was concluded that hydroperoxide
M AN U
decomposition cannot be an important stabilization mechanism of action of HAS.
3.3.3 Quenching of excited oxygen polymer charge transfer complexes. Part of the stabilizing mechanism of HAS in polyolefins was ascribed to the ability of HAS oxygen charge transfer complexes to quench initiating polymer-oxygen charge transfer complexes [47,48,49]. This was concluded from the high efficiency of HAS in preventing the reaction yielding trans-vinylene groups [47], and from the higher
TE D
conversion of oxygen into species that absorb in the carbonyl region of the IR spectra (around 1715 cm-1) for unstabilized than for HAS stabilized PE [48] and PP [49]. On the analogy of singlet oxygen quenching, a mechanism was postulated for the quenching of polymer–oxygen CTCs by primary, secondary and tertiary amine–oxygen
EP
CTCs [21]. Chemical quenching will lead to the destruction of the amine and to the formation of hydrogen peroxide that will initiate new oxidation cycles, consequently these amines cannot act as a stabilizer. If physical quenching is most important an
AC C
improvement in stability can be expected. This is the case for amines that does not contain a α-hydrogen, such as HAS, or cannot form a C=N bond (Scheme 12). For such molecules indeed an increase in UV-stability was observed [21].
SC
RI PT
ACCEPTED MANUSCRIPT
M AN U
Scheme 12. Proposed mechanism for the deactivation of excited primary and secondary amine oxygen CTCs.
4
HAS as long-term heat stabilizer
4.1
Mechanism
TE D
Traditionally phenolic antioxidants are used as long-term heat stabilizer. If phenolic antioxidants are applied a sudden drop of the mechanical properties after an induction time is observed. Instead of phenolic antioxidants, HAS can be applied as long-term heat stabilizer too [6,50,51,52,53,54]. Especially when phenolic antioxidants show drawbacks HAS can be applied [12,55,56].
EP
When HAS is applied as long-term heat stabilizer the decline in properties as a function of time is different from that of polymers containing a phenolic antioxidant. Instead of a
AC C
decrease in properties after an induction period, a (slow) steady decline in the mechanical properties as a function of time is found [54,57,58]. This difference was ascribed to a difference in mechanism of action of phenolic antioxidants and HAS. Model experiments with different hydrocarbons and aldehydes showed that HAS are not capable in reducing the oxidation of hydrocarbons, but they are capable in reducing the oxidation rate in the presence of aldehydes and prevent the formation of peracids [6,25,57], which is in agreement with some of the mechanisms shown above. It was shown that the acceleration of the oxidation of PP can be ascribed to peracids that are formed as a result of the oxidation of aldehydes, which are a result of the oxidation of primary oxidation products [59]. In the presence of HAS the oxidation of the
ACCEPTED MANUSCRIPT
aldehydes is prevented, suggesting that the acceleration of the oxidation is postponed. However, as the HAS does not prevent the formation of hydroperoxides, the polymer continuously oxidizes slowly. In the presence of a phenolic antioxidant the oxidation is ‘stopped’ until the stabilizer is consumed, after which the polymer starts to oxidize and
RI PT
the properties drop. It is known that the initiation of the oxidation process of unstabilized PP is
heterogeneous [34,35,60,61] and spreads from these initiated spots to the surrounding area by infection. Spreading of the degradation from a point where the oxidation is
started has been observed by many researchers [39,62,63]. For PP stabilized with a
SC
phenolic antioxidant a comparable behaviour was observed. After the consumption of the stabilizer the polymer starts to degrade heterogeneous [6,64]. In the presence of
M AN U
HAS the oxidation is not accelerated and the oxidation does not spread. However, the primary oxidation is not stopped, which means that the polymer oxidizes from the beginning resulting in a slow homogeneous degradation [6,64,65]. The differences in behaviour between a phenolic antioxidant (AO-1) and a HAS (HMW-HAS) is visualized in Fig. 2. In the presence of a phenolic antioxidant the degradation (whitening) starts after an induction period and spreads, while in the presence of a HAS a more continuous
307 h
508 h
564 h
682 h
727 h
844 h
AC C
Unaged
EP
TE D
increase in whitening was observed.
Fig. 2. Images, scanned against a black background, of 150 µm thick PP films (4 x 4 cm2) containing 0.1% AO-1 (top row) or 0.1% HAS-2 (bottom row) after oven ageing for different times at 120°C.
4.2
Applications
As mentioned above HAS can be a good alternative for phenolic antioxidants, especially when phenolic antioxidants show drawbacks. An important drawback of phenolic antioxidants is their discoloration [66]. Especially for thin application gas fading can lead
ACCEPTED MANUSCRIPT
to discoloration of phenolic antioxidants [67]. In cases were discoloration of phenolic antioxidants is a problem HAS is a good alternative [68]. In some applications polymers are crosslinked. This is done by adding peroxides or by irradiation, which lead to the formation of radicals that induce crosslinking of the material.
RI PT
As phenolic antioxidants react with radicals their presence cause a reduction in crosslink density and a (partly) consumption of the stabilizer. As HAS stabilizers first have to be
converted into a nitroxide, they do not show this negative influence. For the stabilization of by gamma or e-beam crosslinked irradiation UHMwPE implants, the use of Vitamin E (AO-2) is the state of the art. However, this phenolic antioxidants interferes with the
SC
cross-link chemistry, leading to a lower cross-link density [69,70,71], and its
consumption, which results in a decrease in the concentration and in discolouration. It
M AN U
has been shown that these drawbacks can be overcome by using HAS. The effectivity of HAS is a least as good as that of Vitamin E (AO-2) and due to their different mechanism of action, HAS do not interfere with the cross-link chemistry and does not induce discoloration [56].
HAS as UV-stabilizer
5.1
Mechanism.
TE D
5
The majority of the above described mechanisms describe the radical scavenging ability of HAS. It is clear that at least a part of the high activity of HAS as light stabilizer can be
EP
ascribed to its regenerative stabilization mechanism. However, in contrast to the thermooxidative degradation of PP it is not clear that the formation of peracids plays an important role.
AC C
In the proposed regenerative stabilization mechanisms light seems not to play an important role. One of the few mechanism in which light plays a role is the excited state quenching mechanism, which seems to be important for the stabilization of polyolefins.
5.2
Applications
In cases were photo-oxidation is the most important UV-degradation HAS is by far the best performing stabilizer. For thin applications oligomeric HAS stabilizers are used as the low molecular weight versions are too volatile. However, for thick applications the low
ACCEPTED MANUSCRIPT
molecular weight versions performs best, as they can diffuse from the bulk to the surface and in this way give a better surface protection [72]. In a number of cases synergisms between low and high molecular weight HAS
6
RI PT
stabilizers are mentioned [73,74].
Antagonism and Synergisms with HAS.
In many stabilizer formulations, different types of stabilizers are used. As processing
stabilizer phenolic antioxidants and phosphites are applied, for long-term heat stability
SC
phenolic antioxidants and thio-ethers are used and for UV stability, combinations of HAS with other types of UV stabilizers can be applied. Synergisms as well as antagonisms of HAS stabilizers with the other stabilizers are reported [75,76,77,78,79,80,81,82]. For the
M AN U
antagonism between phenolic antioxidants and HAS the following reasons were postulated [77]: •
A decrease in the formation rate of the nitroxide as a consequence of inhibition of the oxidation by the phenolic antioxidant.
•
Reactions between the nitroxide and the phenolic antioxidant causing an increased consumption of the antioxidant.
Reactions between decomposition products of the phenolic antioxidant
TE D
•
(quinones) leading to deactivation of the nitroxide and acceleration of the decomposition of hydroperoxides by the salt of the HAS and the phenolic
EP
antioxidant [79.]
Dependent on the type of phosphite for combinations of HAS and phosphites, synergisms as well as antagonisms are reported [78,83].
AC C
Sulphur containing stabilizers are in use to increase the long-term heat stability of polymers. It was shown that HAS and sulphur containing stabilizers behave in many cases antagonistic [84], which was ascribed to the formation of a salt between acidic decomposition products of the –S- containing stabilizer and the basic HAS [85] or with the nitroxide itself [86,87]. It was shown that by applying less basic HAS derivatives the deactivation by a sulphur containing stabilizers can be reduced [88].
As many of the HAS stabilizers in use are basic, they will form salts when they are exposed to acids from the surrounding or from other additives as e.g. halogen containing
ACCEPTED MANUSCRIPT
flame retardants [89,90]. It was shown that the exposure of HAS to HCl, HBr and HNO3 had a large negative effect, sulphurous acid was somewhat less detrimental and formic acid, which is the strongest carboxylic acid that can be formed during the oxidation of polyolefins, had no effect [91].
RI PT
In the presence of halogenated flame retardants the activity of HAS is limited [90,92], which is ascribed to the formation of the ammonium salt of the HAS [89,93].
Another antagonistic effect reported is the interaction between agrochemicals and HAS, which caused a reduction of the effectivity of HAS as stabilizers for polymers applied in greenhouses [94]. It was shown that sulphur containing as well as acidic species from
HAS stabilizers were developed [88,97].
SC
pesticides and insecticides can be harmful [95,96].To reduce these problems less basic
M AN U
As mentioned above bridged amines show a synergism with HAS in preventing UVdegradation [98]. In reducing the thermo-oxidative degradation rate, aliphatic amines and HAS showed synergisms [98,99]. The aliphatic amine could be added separately or be a part of the chemical structure of the HAS (as e.g. in HAS-5). This stabilizing action of the aliphatic amine was ascribed to their ability to react with aldehydes and in this way prevent the formation of peracids.
References
TE D
7
1 F. Gugumus, in Oxidation Inhibition In Organic Materials,Vol. II, ed. J. Pospisil and P. P. Klemchuk. CRC Press, Boca Raton, FL, pp. 29-163. 2 H. Zweifel, R. Maier, M. Schiller, Plastics Additives Handbook 6th Edition, Munich: Hanser
EP
Publications; 2009.
3 R. Maier, M. Schiller, Handbuch Kunststoff Additive, Munich: Hanser Publications; 2016.
AC C
4 K. Murayama, T. Yoshioka, Stable free radicals. IV. Decomposition of stable nitroxide radicals, Bull Chem Soc Japan 42 (1969) 2307-2309. 5 T. Toda, T. Kurumada, K. Murayama, Progress in the light stabilization of polymers, Amer Chem Soc Symp Ser 280 (1985) 37-54. 6 P. Gijsman, M. Gitton, Hindered Amine Stabilisers as Long-term Heat Stabilisers for Polypropylene, Polym Degrad Stab 66 (1999) 365-371. 7 G. Balint, A. Rockenbauer, T. Kelen, F. Tudos, L. Jokay, Esr study of polypropylene photo stabilisation by sterically hindered piperidine derivatives, Polym Photochem 1 (1981) 139-152.
ACCEPTED MANUSCRIPT
8 D. K. Hodgeman, Formation of Polymer-Bonded Nitroxyl radicals in the UV Stabilization of Polypropylene by a Bifunctional Hindered Amine light Stabilizer, J Polym Sci Polym Chem Ed 19 (1981) 807-818. 9 J. Pilař, D. Michálková, I. Šeděnková, J. Pfleger, J. Pospíšil, NOR and nitroxide-based HAS in
RI PT
accelerated photooxidation of carbon-chain polymers; Comparison with secondary HAS: An ESRI and ATR FTIR study, Polymer Degradation and Stability 96 (5) (2011) 847-862.
10 J. Pilař, D. Michálková, M. Šlouf, T. Vacková, J. Dybal, Heterogeneity of accelerated
photooxidation in commodity polymers stabilized by HAS: ESRI, IR, and MH study, Polymer Degradation and Stability 103 (1) (2014) 11-25.
SC
11 Yu. B. Shilov, R.M. Battalova, E.T. Denisov, Regeneration of iminoxyl radical during polypropylene oxidation, Doklad Acad Nauk USSR 207 (1972) 388-389.
(1995) 87-189.
M AN U
12 J. Pospíšil, Aromatic and Heterocyclic Amines in Polymer Stabilization, Adv Polym Sci 124
13 J. Sedlar, J. Petruy, J. Pak, M. Navrati, Polymer photostabilization by HAS derivatives: the role of piperidine-hydroperoxide associates, Polymer 21 (1980) 5-7.
14 J. M. Bobbitt, C. Bruckner, N. Merbouh, Oxoammonium- and nitroxide-catalyzed oxidations of alcohols, Org Reactions 74 (2009) 103–424.
15 F. Gugumus, Current trends in mode of action of hindered amine light stabilizers, Polym Degrad Stab 40 (1993) 167-215.
TE D
16 D.J. Carlsson, K.H. Chan, D.M. Wiles, Polypropylene photostabilization by tetramethylpiperidine species. in "Photodegradation and Photostabilisation of Coatings" eds. Pappas, S.R., Winslow, F.H., American Chemical Society Symposium Series No. 151, 1981, pp. 51-63.
17 G. Geuskens, G. Nedelkos, The oxidation of hindered amine light stabilizers to nitroxyl
EP
radicals in solution and in polymer, Polym Degrad Stab 19 (1987) 365-378. 18. T. Toda, E. Mori, K. Murayama, Stable free radicals. IX. Peroxy acid oxidation of hindered
AC C
secondary amines to nitroxide radicals, Bull Chem Soc Jpn 45 (1972) 1904-1908. 19. B. Felder, R. Schumacher, F. Sitek, Hindered Amine Light Stabilizers, A mechanistic study. ACS Symp Ser 280 (1985) 69-90. 20. A. Zahradnickova, J. Sedlar D. Dastych, Peroxy acids in photo-oxidized polypropylene, Polym Deg Stab 32 (1991) 155-176. 21 P. Gijsman, New synergists for Hindered Amine Light Stabilizers, Polymer 43 (2002) 15731579. 22 G. Gryn’ova, K. U. Ingold, M. L. Coote, New Insights into the Mechanism of Amine/Nitroxide Cycling during the Hindered Amine Light Stabilizer Inhibited Oxidative Degradation of Polymers, J. Am. Chem. Soc. 134 (2012) 12979−12988.
ACCEPTED MANUSCRIPT
23 Yu. B. Shilov, E.T. Denisov, Mechanism of the inhibiting activity of iminoxyl radicals during oxidation of polypropylene and polyethylene, Vysokomol. Soyed. A 14 (10) (1974) 2313-2316. 24 T.A.B.M. Bolsman, A.P. Blok, T.H.G. Frijns, Mechanism of the catalytic inhibition of hydrocarbon autoxidation by secondary amines and nitroxides, Rec J Royal Neth Chem Soc 97
RI PT
(1978) 313-319.
25 P.P. Klemchuck, M.E. Gande, Stabilization mechanisms of hindered amines, Polymer Degradation and Stability 22(3) (1988) 241-274.
26 P.P. Klemchuck, M.E. Gande, Hindered Amine Mechanisms: Part III-Investigations using isotopic labelling, Polymer Degradation and Stability 27 (1) (1990) 65-74.
SC
27 E.N. Step, J. Turro, M.E. Gande, P.P. Klemchuck, Flash photolysis and time-resolved electron spin resonance studies triplet benzophenone quenching by hindered amine light stabilizers
Photobiool A: Chem. 74 (1993) 203-210.
M AN U
(HAS). A comparison of HAS amines and aminoethers and hydrogen atom donors, J. Photochem
28 E.N. Step, J. Turro, M.E. Gande, P.P. Klemchuck, Mechanism of Polymer Stabilization by Hindered-Amine Light stabilizers (HAS). Model Investigations of the Interaction of peroxy Radicals with HAS Amines and Amino Ethers, Macromolecules 27 (1994) 2529-2539. 29 D. W. Grattan, D. J. Carlsson, D. M. Wiles, Polyolefin photo-stabilisation mechanisms. Reaction of tetramethylpiperidine derivatives in model systems, Polym Degrad Stab 1 (1979) 6984.
TE D
30 V. Ya. Shlyapintokh, V. B. Ivanoc, Antioxidant action of sterically hindered amines and related compounds in Developments in Polymer Stabilisation Ed. G. Scott, Applied Science Publisher London, Vol. 5 (1982) 41-70.
31 A.L.J. Beckwith, V. W. Bowry, K. U. Ingold, Kinetics of Nitroxide Radical Trapping. 1. Solvent
EP
Effects, J. Am Chem Soc 114 (1992) 4983-4992. 32 V. W. Bowry, K. U. Ingold, Kinetics of Nitroxide Radical Trapping. 2. Structural Effects, J. Am Chem Soc 114 (1992) 4992-4996.
AC C
33 A. Garton, D.J. Carlsson, D.M. and Wiles, Polymer Oxidation and Secondary Cage Combination of Peroxyl Radicals, Makromol Chem 181 (1980), 1841-1846. 34 P. Richters, Initiation process in the oxidation of polypropylene, Macromolecules 3 (1970) 262264.
35 J.B. Knight, P.D. Calvert and N.C. Billingham, Localization of oxidation in polypropylene, Polymer 26 (1985), 1713-1718. 36 G.A. George, M. Celina, C. Lerf, G. Cash and D. Wendell, A spreading model for the oxidation of polypropylene, Macromol Symp 115 (1997) 68–92. 37 M. Celina and G.A. George, Heterogeneous and homogeneous kinetic analysis of the thermal oxidation of polypropylene, Polym Degrad Stab 50 (1995) 89–99.
ACCEPTED MANUSCRIPT
38 I. Blakey and G.A. George, Raman spectral mapping of photo/oxidised polypropylene, Polym Degrad Stab 70 (2000) 269–275. 39 G. Ahlblad, P. Gijsman, B. Terselius, A. Jansson and K. Möller, Thermo-oxidative stablility of PP waste films as studied by imaging chemiluminescence, Polym Degrad Stab 73 (2001) 15–22.
RI PT
40 A.A. Oswald, F. Noel, A.J. Stephenson, Organic sulfur compounds. V. Alkylammonium thiolate and peroxide salts; possible intermediates in amine-catalyzed oxidation of mercaptans by hydroperoxides, J Org Chem 26 (1961) 3969-3974.
41 D.W. Grattan, A.H. Reddoch, D.J. Carlsson, D.M. Wiles, Polymer photostabilization by
piperidine derivatives: the role of nitroxide-hydroperoxide complexing, J Polym Sci: Polym Lett
SC
Ed 16 (1978) 143-148.
42 F. Gugumus. Developments in the U.V.-stabilisation of polymers,in Developments in Polymer Stabilisation Ed. G. Scott, Applied Science Publisher London, Vol. 1 (1979) 261-308.
M AN U
43 M. G. Chan, Metal deactivators, in Oxidation Inhibition in Organic Materials Vol 1 Eds J. Pospisil, P. P. Klemchuck, CRC Press Inc Boca Raton, Florida (1990) pp. 225-246. 44 S.P. Fairgrieve, J.R. Mac Callum, Photostabilization by hindered amines: the role of transition metal complexation, Polymer Communications 25 (2) (1984) 44-6.
45 S.P. Fairgrieve, J.R. Mac Callum, Hindered Amine Light Stabilizers: A proposed photostabilization mechanism, Polym Degrad Stab 8 (1984) 107-121.
46 J. Sedlar, J. Petruj, J. Pac, A. Zahradnicova, Photostabilizing action of sterically hindered
662.
TE D
piperidines-1, peroxide decomposing and hydrogen donating ability, Eur. Polym J 16 (1980) 659-
47 F. Gugumus, Findings pertaining to polyethylene photooxidation, Makromol. Chem. Macromol. Symp. 25 (1989) 1-22.
48 P. Gijsman, J. Hennekens and D. Tummers, The mechanism of action of hindered amine light
EP
stabilizers, Polym Degrad Stab 39 (1993) 225–233. 49 P. Gijsman, A. Dozeman, Comparison of the UV-degradation chemistry of unstabilized and
AC C
HAS-stabilized polyethylene and polypropylene, Polym Degrad Stab 53 (1996) 45-50. 50 Th. Schmutz, E. Kramer, H. Zweifel, G. Dorner, Advanced extraction resistant long-term thermal stabilizers for polyolefin pipes, Journal of Elastomers and Plastics 30 (1) (1998) 55-67. 51 V. Malatesta, L. Davis, J. Zenner, High heat and UV-stabilization of polyolefins under demanding conditions. Addcon World 2005, International Conference, 11th, Hamburg, Germany, Sept. 21-22, 2005 (2005) Paper 7/1-Paper 7/11. 52 C.M. Liauw, A. Quadir, N.S. Allen, M. Edge, A. Wagner, Effect of hindered piperidine light stabilizer molecular structure and UV-absorber addition on the oxidation of HDPE. Part 1: Longterm thermal and photo-oxidation studies, Journal of Vinyl & Additive Technology 10 (2) (2004) 79-87.
ACCEPTED MANUSCRIPT
53 F. Gugumus, Advances in the stabilization of polyolefins. Polymer Degradation and Stability 24 (4) (1989) 289-301. 54 F. Gugumus, Mechanisms of thermooxidative stabilization with HAS, Polym. Degrad Stab. 44 (1994) 299–322.
Polymers, Luzern (1992), Proceedings pp 57.
RI PT
55 W.O. Drake, Fourteenth International Conference on the Stabilization and Degradation of
56 P. Gijsman, H.J. Smelt, D. Schumann, Hindered amine light stabilizers: An alternative for radiation cross-linked UHMwPE implants, Biomaterials 31 (26) (2010) 6685-6691.
stabilizers, Polym. Deg. Stab. 43 (1994) 171-176.
SC
57 P. Gijsman, The mechanism of action of hindered amine stabilizers (HAS) as long-term heat
58 W.W. Müller, I. Jakob, R. Tatzky-Gerth, A. Wöhlecke, A study on antioxidant depletion and
Eng Sci 56 (2016) 129–142.
M AN U
degradation in polyolefin-based geosynthetics: Sacrificial versus regenerative stabilization. Polym
59 P. Gijsman, J. Hennekens and J. Vincent, The mechanism of the low temperature oxidation of polypropylene, Polym. Deg. Stab. 42 (1993) 95-105.
60 N.C. Billingham, Localization of oxidation in polypropylene, Makromol Chem Macromol Symp 28 (1989) 145-163.
61 I. Blakey, N.C. Billingham, G.A. George, Use of 9,10-diphenylanthracene as a contrast agent in chemiluminescence imaging: The observation of spreading of oxidative degradation in thin
TE D
polypropylene films, Polymer Degradation and Stability 92(11) (2007) 2102-2109. 62 P. Eriksson, T. Reitberger, B. Stenberg, Gasphase distribution to the spreading of oxidation in PP as studied by imaging Chemiluminescence, Polym. Degrad. Stab. 78 (2002) 183-189. 63 M. Celina, R.L. Clough, G.D. Jones, Initiation of polymer degradation via transfer of infectious species, Polym. Degrad. Stab 91 (2006) 1036-1044.
EP
64 M. Hamskog, B. Terselius, P. Gijsman, Mapping of heterogeneous degradation of polypropylene using Imaging Chemiluminescence, Polym. Deg. Stab. 82 (2003) 181-186.
AC C
65 P. Gijsman, Mechanism of the thermo-oxidative degradation of unstabilized, phenolic antioxidant and hindered amine stabilizer containing polypropylene” in “Specialty Polymer Additives” eds S. Al-Malaika, A. Golovoy, C.A. Wilkie, Blackwell Science, Oxford, 2001 pp 67-90. 66 J. Pospisil, W.-D Habicher, J. Pilar, S. Nespurek, J. Kuthan, G-O Piringer, H. Zweifel, Discoloration of polymers by phenolic antioxidants, Polymer Degradation and Stability 77 (3) (2002) 531-538.
67 R.V. Todesco, R. Diemunsch, T. Franz, New developments in the stabilization of PP fibers for automotive applications Chemiefasern/Textilindustrie, 43 (10) (1993), E135-E137, T197-T199. 68 P. Solera, New trends in polymer stabilization, Journal of Vinyl & Additive Technology 4 (3) (1998) 197-210.
ACCEPTED MANUSCRIPT
69 E. Oral, C. Godleski Beckos, A.S. Malhi, O.K. Muratoglu. The effects of high dose irradiation on the cross-linking of vitamin E-blended ultrahigh molecular weight polyethylene, Biomaterials 29 (2008) 3557-60. 70 M. Parth, N. Aust, K. Lederer, Studies on the effect of electron beam radiation on the
RI PT
molecular structure of ultra-high molecular weight polyethylene under the influence of alphatocopherol with respect to its application in medical implants. Journal of Materials Science: Materials in Medicine 13 (2002) 917-21.
71 E. Oral, E.S. Greenbaum, A.S. Malhi, W.H. Harris, O.K. Muratoglu, Characterization of irradiated blends of alpha-tocopherol and UHMWPE, Biomaterials 26 (2005) 6657-63.
SC
72 P. Delprat, X. Duteurtre, J-L. Gardette, Photo-oxidation of unstabilized and HALS-stabilized polyphasic ethylene-propylene polymers, Polym Degrad Stab 50 (1995) 1-12.
Stability 44 (3) (1994) 273-97.
M AN U
73 F. Gugumus, New trends in the stabilization of polyolefin fibers, Polymer Degradation and
74 F. Gugumus, Possibilities and limits of synergism with light stabilizers in polyolefins 1. HALS in polyolefins, Polymer Degradation and Stability 75(2) (2002) 295-308.
75 N.S. Allen, J.F. McKellar, Photostabilization of commercial polypropylene by hindered piperidine compounds, Plast Rubber Mat Applicat, Nov 1979 170-174. 76 N.S. Allen, Photo-stabilising performance of a hindered piperidine compound in polypropylene film: anti-oxidant/light stabiliser effects, Polym Degrad Stab 2 (1980) 129-135.
TE D
77 J. Lucki, J.F. Rabek, B Ranby, Photostabilizing Effect of Hindered Piperidine Compounds: lnteraction Between Hindered Phenols and Hindered Piperidines, Polym Photochem 5 (1984) 351-354.
78 N.S. Allen, A. Hamid, F.L. Loffelman, P. Macdonald, M. Rauhut, P.V. Sushi, Interactions of antioxidants with hals in the thermal and photochemical oxidation of pp film, Plast Rubber
EP
Process Applicat 5 (1985) 259-265.
79 H. Yamashita, Y. Ohkatsu, A new antagonism between hindered amine light stabilizers and
AC C
acidic compounds including phenolic antioxidants, Polym Degrad Stab 80 (2003) 421–426. 80 J E. Volponi, L.H.I. Mei, D. dos Santos Rosa, The use of differential photocalorimetry to measure the oxidation induction time of isotatic polypropylene, Polymer Testing 23 (2004) 461465.
81 P. Gijsman, J. Sampers, W. Bunge, J. Vaassen, Stabilized polypropylene resin composition, EP1340789.
82 L. Maringer, L. Roiser, G. Wallner, N. Gernot, D. Nitsche, W. Buchberger, The role of quinoid derivatives in the UV-initiated synergistic interaction mechanism of HALS and phenolic antioxidants, Polymer Degradation and Stability 131 (2016) 91-97.
ACCEPTED MANUSCRIPT
83 I. Bauer, W.D. Habicher, S. Korner, S. Al-Malaika, Antioxidant interaction between organic phosphites and hindered amine light stabilizers: effects during photoxidation of polypropylene-II, Polym Degrad Stab 55 (1997) 217-224. 84 S. W. Bigger, O Delatycki, The effect of hindered amine light stabilizers on the photoxidative
RI PT
stability of high density polyethylene, J Polym Sci A Polym Chem 27 (1989) 63-73.
85 L. Yu. Smoliak, N. R. Prokopchuck, Y. P. Losev, V. P. Prokopovich, I. A. Klimotsova,The role of sulphur containing groups in inhibition of oxidative degradation of polyolefins by HALS, Polym Blends Polym Composit 1 (2002) 151-159.
86 K. Kikkawa, Y. Nakahara, Antagonism between hindered amine light stabilizers and sulphur-
SC
containing compounds, Polym Degrad Stab 18 (1987) 237-245.
87 J. Lucki, S. Z. Jian, J. F. Rabek, B. Ranby, Antagonistic Effects of Hindered Piperidines and
27-47.
M AN U
Organic Sulphides in Photostabilization of cis –1,4- Polybutadiene, Polym Photochem 7 (1986)
88 R.L. Gray, Additives: a novel non reactive HALS Boosts polyolefin stability, Plast Eng 47 (6) (1991) 21-23.
89 J-L. Gardette, C. Sinturel, J. Lemaire, Photooxidation of fire retarded polypropylene, Polym Degrad Stab 64 (1999) 411-417.
90 K. Antos, J. Sedlar, Influence of brominated flame retardant thermal decomposition products on HALS, Polym Degrad Stab 90 (2005) 188-194.
TE D
91 D.J. Carlsson, K. Zhang, D.M. Wiles, Polypropylene Photostabilization by Hindered Amines in the Presence of Acidic Species J Appl Polym Sci 33 (1987) 875-884. 92 R.L. Gray, R.E. Lee, UV stabilization of polypropylene fiber containing organic bromine flame th
retardants Annual Technical Conference - Society of Plastics Engineers 54 (Vol 3) (1996), 30283032.
EP
93 C. Sinturel, J. Lemaire, J-L Gardette, Photooxidation of fire retarded polypropylene. III. Mechanism of HAS inactivation, European Polymer Journal 36 (7) (2000) 1431-1443.
AC C
94 J.H. Khan, S.H. Hamid, Durability of HALS-stabilized polyethylene film in a greenhouse environment, Polym Deqrad Stab 48 (1995) 137-142. 95 E. Epacher, B, Pukanszky, Interactions of pesticides and stabilizers in PE films for agricultural use, Antec (1999) 3785-3790. 96 J-R. Pauquet, Technological advances in the stabilization of polyethylene films, Plast Rubber Composit Process Applications 27 (1998) 19-24. 97 P. Solera, G. Capocci, Designing higher performance: A new light stabilizer for polyolefins Polyolefins 2000, International Conference on Polyolefins, Houston, TX, United States, Feb. 27Mar. 1, 2000 (2000), 699-713.
ACCEPTED MANUSCRIPT
98 P. Gijsman. M. Gitton, Aliphatic Amines for use as Long-term Heat Stabilisers for Polypropylene, Polym. Deg. Stab. 81 (2003) 483-489. 99 A. Rosales Jasso, M.L. Berlanga Duarte, N.S. Allen. Synergistic Effect between Hindered
AC C
EP
TE D
M AN U
SC
Applied Polymer Science 92 (2004) 280–287.
RI PT
Amine Light Stabilizers and Partially Hindered Oligomeric Amines in Polyethylene, Journal of
ACCEPTED MANUSCRIPT
8
Appendix
Abbreviation Chemical structure
Trade name(s) ( Supplier)
RI PT
Anox® PP18 (Addivant) Irganox® 1076 (BASF)
AO-1
Songnox® 1076 (Songwon) Thanox® 1076 (Rianlon)
SC
Irganox® E201 (BASF)
AO-2
Quali®-E (DSM)
N H
HAS-1
M AN U
Lowillite® 77 (Addivant)
O
O
O
O
Sabo® stab UV 70 Songlight® 7700 (Songwon) Tinuvin® 770 (BASF)
H N
AC C
HAS-3
EP
HAS-2
TE D
Chimassorb® 944 (BASF) Lowilite® 94 (Addivant) Sabo® stab UV 944 (Sabo) Songlight® 9440 (Songwong)
BLS® 123 (Mayzo) Milestab® 123 (MPI Chemie) Omnistab® LS 123 (Deltachem (QingDao) Tinuvin® 123 (BASF)
ACCEPTED MANUSCRIPT
Abbreviation Chemical structure
Trade name(s) ( Supplier) CH3 N
Lowilite 92 (Addivant) O
HAS-4
O O
Milestab® 765 (MPI Chemie) Sabo® Stab UV 65 (Sabo)
RI PT
O
CH3 R R
HN NH
R N N
Lowilite® 19 (Addivant)
R
Sabo® stab UV 119 (Sabo)
C4H9
R=
N N
M AN U
HAS-5
Songlight® 1190 (Songwong)
N N
N
N C4H9 N
CH3
EP
TE D
CH3
AC C
SC
Tinuvin® 765 (BASF) N
S0141-3910(17)30135-0
DOI:
10.1016/j.polymdegradstab.2017.05.012
Reference:
PDST 8231
To appear in:
Polymer Degradation and Stability
Received Date: 20 March 2017 Revised Date:
4 May 2017
Accepted Date: 17 May 2017
Please cite this article as: Gijsman P, A review on the mechanism of action and applicability of Hindered Amine Stabilizers, Polymer Degradation and Stability (2017), doi: 10.1016/ j.polymdegradstab.2017.05.012. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
A review on the mechanism of action and applicability of Hindered Amine Stabilizers
RI PT
Pieter Gijsman
DSM Ahead b.v., P.O. Box 18, 6160 MD Geleen, The Netherlands Tel.: 0031 46 4761538. E-mail address: [email protected]
1
SC
Key words: UV-stability, long-term heat stability, antagonism, synergisms, HALS, HAS
Abstract
M AN U
Hindered Amine Stabilizers (HAS) are by far the best performing UV-stabilizers and in a number of applications they are the best performing long-term heat stabilizer too. In this paper an overview is given of the different mechanisms proposed that can explain the high activity as well as the applicability of HAS as UV-stabilizer and as long-term heat stabilizer.
2
Introduction
TE D
After the introduction of the first hindered amine light stabilizer (HALS) in the 1970ths, they rapidly became the most important UV-stabilizer for the majority of plastics. Due to their high activity they are nowadays in use for the light stabilization of many organic polymers (e.g. polyethylene, polypropylene, thermoplastic polyolefins and elastomers,
EP
coatings, styrenic polymers, polyamides, polyurethanes, polyacetals adhesives and sealants). Without the discovery of HALS the outdoor applicability of many polymers
3.
AC C
would be limited. The good performance of HAS is clearly shown in references 1, 2 and
The invention of HALS was based on the discovery that the 2,2,6,6-tetramethyl-1piperidinyloxy free radical ((TEMPO) Fig. 1) is a very effective radical scavenger [4,5]. However, due to its physical and chemical properties TEMPO itself cannot be applied. TEMPO is coloured, and thus will discolour a polymer, it is thermally unstable and volatile [5]. It can also react with phenolic antioxidants present in many polymers as processing and/or long-term heat stabilizer. The discovery that compounds in which the N-oxyl functionality was replaced by a N-H functionality also showed good UV
ACCEPTED MANUSCRIPT
stabilization activity was the key finding that led to the development of HALS stabilizers [5].
O Fig. 1. Chemical structure TEMPO
RI PT
N
SC
Although HALS stabilizers were developed as UV-stabilizer, it is more and more
recognized that these molecules could also impart long-term heat stability. Especially when phenolic antioxidants cannot be used due to secondary reasons as e.g.
M AN U
discolouration, HALS is used to protect polymers against long-term heat degradation [6]. Consequently the in use abbreviation was changed from HALS (Hindered Amine Light Stabilizer) into HAS (Hindered Amine Stabilizer).
Nowadays there are many HAS stabilizers commercial of which the majority are based on 2,2,6,6-tetra-methyl-4-piperidinyl derivatives. An overview of the chemical structures as well as a non-comprehensive list of brand names and suppliers of the HAS and the
TE D
other stabilizers mentioned in this paper is given in Appendix 1. The first commercial HAS (HAS-1) is relatively low in molecular weight, which means that due to its high volatility it is not suitable for thin applications. To overcome this problem oligomeric HAS types (as e.g. HAS-2) were developed. One of the drawbacks of the piperidinyl moiety of HAS stabilizers is that it is basic, which means that it can react with acids and forms a
EP
not stabilizing salt. Consequently, the effectiveness of HAS in systems where acids are present or can be formed is limited. To beat this problem less basic HAS stabilizers as
AC C
e.g. N-O-R types were developed, a commercial example is HAS-3. Since the discovery of HAS, a lot of research was done on their mechanism of action and many different mechanisms were proposed. At the moment, there is still no consensus, which might be related to the fact that the mechanism of action of HAS is circumstances dependant. So are results of the mechanism of action in different polymers, from UV-degradation with different light sources and even from thermooxidative degradation compared. In the following an overview of the proposed mechanisms of action and the applicability of HAS is given.
ACCEPTED MANUSCRIPT
3
Mechanism of action of HAS Since the discovery of HAS stabilizers, a lot of research was done on their
mechanism of action and many different mechanisms were proposed. ESR studies on the stabilizing activity of HAS showed that the piperidinyl moiety
RI PT
(amine) is easily converted in a piperidinoxyl radical (nitroxide) [7,8,9,10]. Together with the knowledge that these radicals are stable and excellent alkyl radical scavengers, it was easily concluded that they play an important role in their stabilizing activity. Shilov et al. [11] detected the consumption of nitroxide during the cumyl
hydroperoxide initiated degradation of PP in an argon atmosphere, whereas in this
SC
experiment the addition of oxygen led to an increase of the nitroxide concentration. From this it was concluded that the nitroxide can be regenerated, which could explain the high
M AN U
effectiveness of HAS. After this discovery a lot of research was done on the mechanism of action of HAS and several mechanism were proposed. The majority of these mechanisms are based on radical scavenging in which the formation of the nitroxide as well as its regeneration plays a key role. In the following an overview of the proposed nitroxide formation and regeneration mechanisms as well as other possible HAS
3.1
TE D
stabilization mechanisms is given.
Nitroxide formation mechanisms
For the conversion of HAS to the corresponding nitroxide several mechanism were proposed. In the majority of these mechanisms the amine is oxidized by polymer
EP
oxidation products, which is in agreement with the observation that the stabilization effect of HAS only start after some accumulation of hydroperoxides [12,13]. For this
AC C
conversion the absence of α-hydrogens in the amine is essential, as otherwise the amine is converted into a nitrone [14]. Thus, although these stabilizers are called Hindered Amines, the function of the 4 methylene groups is not introducing steric hindrance, but eliminating α-hydrogens. It was postulated that the nitroxide is formed by a reaction of a hydroperoxide
with the amine followed by the reaction of the formed alkoxyamine with a peroxy radical [13]. Alternatively a hydroxyl amine is formed that is transformed into the nitroxide (Scheme 1), which of these two reactions is preferred depend on the polymer type [15].
ACCEPTED MANUSCRIPT
N - H2O
+ ROOH N
O
or
+ ROO - ROOR
R + ROO
- ROH
N O
RI PT
- ROOH
H N OH
Scheme 1. Possible reactions of a hindered amine to a hydroxyl or
SC
alkyloxyamine
Alternatively the nitroxide is formed from the reaction of the amine with a peroxy
M AN U
radical leading to an aminyl radical that in a sequence of oxidation reactions is transferred into a nitroxide (Scheme 2) [16].
O N
2
O / H R
N
H 2 O R +
2
O R + H N
Scheme 2. Reaction of a hindered amine with a peroxy radical leading to a
TE D
nitroxide [16].
EP
H O R +
2
O R + H N
O N
It was also suggested that the nitroxide directly can be formed from the reaction of a hindered amine with a peroxy radical, which lead to a nitroxide and an alcohol (Scheme 3 [17]).
AC C
Scheme 3. Formation of a nitroxide from the reaction between a hindered amine and a peroxy radical [17].
It was also proposed that the formation of the nitroxide can be a result of a reaction of the amine with oxidation products that are formed. Toda et al. [18] assumed that the nitroxide is formed by a reaction of a peracid with the hindered amine (Scheme 4) and Felder [19] suggested a reaction between an acylperoxy radical and the hindered amine to form the nitroxide and an acid (Scheme 5).
ACCEPTED MANUSCRIPT
Zahradnickova et al. [20] showed that the nitroxide indeed can be formed by the reaction of the amine with oxidized polypropylene (PP) containing peracids.
RI PT
O 2 H + O N
2 + H O
O C
R 3
H O
O
O C
R 3 + H N
2
Scheme 4. Formation of the nitroxide according to Toda et al .[18].
M AN U
SC
O N
+ H O
O C
R
O
O
O C
R + H N
Scheme 5. Formation of the nitroxide according to Felder [19]
More recently it was suggested that the nitroxide can be formed from its charge
EP
TE D
transfer complex with oxygen (Scheme 6 [21]).
Scheme 6. Formation of the nitroxide from the excited charge transfer complex of
AC C
the amine with oxygen [21]
The majority of the commercially available hindered amine stabilizers are secondary amines, however in some cases tertiary amines (>N-CH3) are used (e.g. HAS-4). The transformation of the tertiary amine to the nitroxide is more complicated. The most logical explanation is that the tertiary amine is first oxidized to a secondary amine, from which the nitroxide is formed [12]. This mechanism was confirmed with high-level ab initio molecular orbital theory calculations [22].
ACCEPTED MANUSCRIPT
3.2
Nitroxide regeneration mechanisms
The high activity of hindered amine stabilizers was ascribed to the possibility that the formed nitroxide can be regenerated in a cyclic reaction [11]. The mechanism causing this regeneration is still under debate and many variations are proposed. Shilov and
RI PT
Denisov [23] proposed that the nitroxide is regenerated in a reaction between the
M AN U
SC
aminoether and a peroxy radical, this reaction is called the ‘Denisov cycle’ (Scheme 7).
Scheme 7. Nitroxide regeneration mechanism according to the Denisov cycle.
There are many variations on the Denisov cycle suggested, but all of them are based on
TE D
the regeneration of the nitroxide. According to Bolsman [24] the cyclic mechanism that is responsible for the catalytic scavenging of tertiary alkyl and peroxy radicals involves the
AC C
EP
formation of a hydroxylamine from the alkyloxyamine (Scheme 8).
Scheme 8. Nitroxide regeneration involving the formation of a hydroxyl amine [24]
ACCEPTED MANUSCRIPT
It was shown that HAS stabilizers are effective in model systems that can form peracids [25,26], it was also shown that peracids play an important role in the thermo-oxidative degradation of PP [6]. According to Step et al. [27,28] peracyl radical plays a key role in
M AN U
SC
RI PT
the nitroxide regeneration mechanism (Scheme 9).
TE D
Scheme 9. Nitroxide regeneration involving peracyl radicals [27,28].
Using high-level ab initio molecular orbital theory calculations of the free energy barriers and reaction energies in the gas phase and in solution, a comparison between the
EP
different postulated mechanisms was made [22]. Based on this calculations it was concluded that the nitroxide regeneration reaction depends on the absence or presence of β-or γ-hydrogen atoms in the alkoxy amine (Scheme 10). However, for the reaction
AC C
rate, besides the reaction constant, the concentration of reagents is important too, some of the concentrations of species mentioned in this mechanism are expected to be that low that these reactions does not seem very likely.
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Scheme 10. Nitroxide regeneration mechanism for alkoxyamines with a β- (top) or γ-
TE D
(bottom) hydrogen atom [22]
In all the nitroxide regeneration mechanisms shown above the nitroxide reacts with an alkyl radical, this reaction is in competition with the extremely fast reaction between an alkyl radical and oxygen (kO2) (Scheme 11). The reaction rate between the nitroxide and
EP
an alkyl radical (kNO) was investigated by several groups. It was shown that kNO/ kO2 is
AC C
about 0.1 to 0.25 [29,30,31,32].
Scheme 11. Competition reactions between an alkyl radical and oxygen or a nitroxide radical
ACCEPTED MANUSCRIPT
For the relative reaction rates, the ratio between the concentrations of oxygen and nitroxide is important too. For polyolefins, it was shown that the concentration of the nitroxide is an order of magnitude smaller than that of oxygen, which means that only
RI PT
about 1-2.5% of the alkyl radicals reacts with the nitroxide instead of reacting with oxygen. Consequently the kinetic chain length (amount of times an alkyl radical will
propagate before it terminates) becomes 40-100, which still is small in comparison to the for free radicals in PP published value of 1.75 104 [33]. This shows that even when the
concentration of the nitroxide is limited, it still can reduce the kinetic chain length largely.
SC
Above consideration assumes a homogenous distribution of the nitroxide, however it is shown that degradation is a heterogeneous process [34,35,36,37,38,39]. If the HAS or
M AN U
its nitroxide concentrate in these oxidizing areas, their concentration increases causing an increased alkyl radical scavenging rate. A possibilities for an increased concentration in the oxidizing zones is the formation of associates between hydroperoxides and HAS. Associates between amines and hydroperoxide were reported [13,40]. In model experiments Grattan et al. [41] found for zones being equimolar in hydroperoxide and alkane segments a 26 fold increase in the concentration of nitroxide radicals. From this result it was suggested that association through hydrogen bonding, between the
TE D
nitroxide and hydroperoxides, causing an increase of the local nitroxide concentration to a level at which the reaction of the nitroxide with an alkyl radical could successfully compete with the reaction of an alkyl radical with oxygen. Another possibility for the increased concentration of nitroxides in oxidized zones is the
3.3
EP
formation of charge transfer complexes between peroxy radicals and HAS [42].
Other possible stabilization mechanisms
AC C
Besides the above mentioned radical scavenging activity of HAS a number of potential additional stabilizing roles of HAS are published. These roles are described below.
3.3.1 Transition metal complexation. It is well known that transition metals can initiate the photo-oxidation of polymers, by catalysing the hydroperoxide decomposition [43]. Fairgrieve and McCallum [44,45] showed that HAS is capable in complexing transition metals. This complexation can cause a decrease in the decomposition rate of hydroperoxides into initiating radicals.
ACCEPTED MANUSCRIPT
Moreover, due to complexation of initiating transition metals an increased concentration of HAS in the oxidizing zones can be expected.
RI PT
3.3.2 Hydroperoxide decomposition In Scheme 1 the decomposition of a hydroperoxide by a HAS is depicted, this reaction
can lead to an increase in stability too. However, it is shown that piperidinyl derivatives have hardly any influence on the photolysis rate of t-butylhydroperoxide in an inert
environment [25,46], nor on the decomposition of cumyl hydroperoxide at 120°C in
SC
chlorobenzene [25]. From these results, it was concluded that hydroperoxide
M AN U
decomposition cannot be an important stabilization mechanism of action of HAS.
3.3.3 Quenching of excited oxygen polymer charge transfer complexes. Part of the stabilizing mechanism of HAS in polyolefins was ascribed to the ability of HAS oxygen charge transfer complexes to quench initiating polymer-oxygen charge transfer complexes [47,48,49]. This was concluded from the high efficiency of HAS in preventing the reaction yielding trans-vinylene groups [47], and from the higher
TE D
conversion of oxygen into species that absorb in the carbonyl region of the IR spectra (around 1715 cm-1) for unstabilized than for HAS stabilized PE [48] and PP [49]. On the analogy of singlet oxygen quenching, a mechanism was postulated for the quenching of polymer–oxygen CTCs by primary, secondary and tertiary amine–oxygen
EP
CTCs [21]. Chemical quenching will lead to the destruction of the amine and to the formation of hydrogen peroxide that will initiate new oxidation cycles, consequently these amines cannot act as a stabilizer. If physical quenching is most important an
AC C
improvement in stability can be expected. This is the case for amines that does not contain a α-hydrogen, such as HAS, or cannot form a C=N bond (Scheme 12). For such molecules indeed an increase in UV-stability was observed [21].
SC
RI PT
ACCEPTED MANUSCRIPT
M AN U
Scheme 12. Proposed mechanism for the deactivation of excited primary and secondary amine oxygen CTCs.
4
HAS as long-term heat stabilizer
4.1
Mechanism
TE D
Traditionally phenolic antioxidants are used as long-term heat stabilizer. If phenolic antioxidants are applied a sudden drop of the mechanical properties after an induction time is observed. Instead of phenolic antioxidants, HAS can be applied as long-term heat stabilizer too [6,50,51,52,53,54]. Especially when phenolic antioxidants show drawbacks HAS can be applied [12,55,56].
EP
When HAS is applied as long-term heat stabilizer the decline in properties as a function of time is different from that of polymers containing a phenolic antioxidant. Instead of a
AC C
decrease in properties after an induction period, a (slow) steady decline in the mechanical properties as a function of time is found [54,57,58]. This difference was ascribed to a difference in mechanism of action of phenolic antioxidants and HAS. Model experiments with different hydrocarbons and aldehydes showed that HAS are not capable in reducing the oxidation of hydrocarbons, but they are capable in reducing the oxidation rate in the presence of aldehydes and prevent the formation of peracids [6,25,57], which is in agreement with some of the mechanisms shown above. It was shown that the acceleration of the oxidation of PP can be ascribed to peracids that are formed as a result of the oxidation of aldehydes, which are a result of the oxidation of primary oxidation products [59]. In the presence of HAS the oxidation of the
ACCEPTED MANUSCRIPT
aldehydes is prevented, suggesting that the acceleration of the oxidation is postponed. However, as the HAS does not prevent the formation of hydroperoxides, the polymer continuously oxidizes slowly. In the presence of a phenolic antioxidant the oxidation is ‘stopped’ until the stabilizer is consumed, after which the polymer starts to oxidize and
RI PT
the properties drop. It is known that the initiation of the oxidation process of unstabilized PP is
heterogeneous [34,35,60,61] and spreads from these initiated spots to the surrounding area by infection. Spreading of the degradation from a point where the oxidation is
started has been observed by many researchers [39,62,63]. For PP stabilized with a
SC
phenolic antioxidant a comparable behaviour was observed. After the consumption of the stabilizer the polymer starts to degrade heterogeneous [6,64]. In the presence of
M AN U
HAS the oxidation is not accelerated and the oxidation does not spread. However, the primary oxidation is not stopped, which means that the polymer oxidizes from the beginning resulting in a slow homogeneous degradation [6,64,65]. The differences in behaviour between a phenolic antioxidant (AO-1) and a HAS (HMW-HAS) is visualized in Fig. 2. In the presence of a phenolic antioxidant the degradation (whitening) starts after an induction period and spreads, while in the presence of a HAS a more continuous
307 h
508 h
564 h
682 h
727 h
844 h
AC C
Unaged
EP
TE D
increase in whitening was observed.
Fig. 2. Images, scanned against a black background, of 150 µm thick PP films (4 x 4 cm2) containing 0.1% AO-1 (top row) or 0.1% HAS-2 (bottom row) after oven ageing for different times at 120°C.
4.2
Applications
As mentioned above HAS can be a good alternative for phenolic antioxidants, especially when phenolic antioxidants show drawbacks. An important drawback of phenolic antioxidants is their discoloration [66]. Especially for thin application gas fading can lead
ACCEPTED MANUSCRIPT
to discoloration of phenolic antioxidants [67]. In cases were discoloration of phenolic antioxidants is a problem HAS is a good alternative [68]. In some applications polymers are crosslinked. This is done by adding peroxides or by irradiation, which lead to the formation of radicals that induce crosslinking of the material.
RI PT
As phenolic antioxidants react with radicals their presence cause a reduction in crosslink density and a (partly) consumption of the stabilizer. As HAS stabilizers first have to be
converted into a nitroxide, they do not show this negative influence. For the stabilization of by gamma or e-beam crosslinked irradiation UHMwPE implants, the use of Vitamin E (AO-2) is the state of the art. However, this phenolic antioxidants interferes with the
SC
cross-link chemistry, leading to a lower cross-link density [69,70,71], and its
consumption, which results in a decrease in the concentration and in discolouration. It
M AN U
has been shown that these drawbacks can be overcome by using HAS. The effectivity of HAS is a least as good as that of Vitamin E (AO-2) and due to their different mechanism of action, HAS do not interfere with the cross-link chemistry and does not induce discoloration [56].
HAS as UV-stabilizer
5.1
Mechanism.
TE D
5
The majority of the above described mechanisms describe the radical scavenging ability of HAS. It is clear that at least a part of the high activity of HAS as light stabilizer can be
EP
ascribed to its regenerative stabilization mechanism. However, in contrast to the thermooxidative degradation of PP it is not clear that the formation of peracids plays an important role.
AC C
In the proposed regenerative stabilization mechanisms light seems not to play an important role. One of the few mechanism in which light plays a role is the excited state quenching mechanism, which seems to be important for the stabilization of polyolefins.
5.2
Applications
In cases were photo-oxidation is the most important UV-degradation HAS is by far the best performing stabilizer. For thin applications oligomeric HAS stabilizers are used as the low molecular weight versions are too volatile. However, for thick applications the low
ACCEPTED MANUSCRIPT
molecular weight versions performs best, as they can diffuse from the bulk to the surface and in this way give a better surface protection [72]. In a number of cases synergisms between low and high molecular weight HAS
6
RI PT
stabilizers are mentioned [73,74].
Antagonism and Synergisms with HAS.
In many stabilizer formulations, different types of stabilizers are used. As processing
stabilizer phenolic antioxidants and phosphites are applied, for long-term heat stability
SC
phenolic antioxidants and thio-ethers are used and for UV stability, combinations of HAS with other types of UV stabilizers can be applied. Synergisms as well as antagonisms of HAS stabilizers with the other stabilizers are reported [75,76,77,78,79,80,81,82]. For the
M AN U
antagonism between phenolic antioxidants and HAS the following reasons were postulated [77]: •
A decrease in the formation rate of the nitroxide as a consequence of inhibition of the oxidation by the phenolic antioxidant.
•
Reactions between the nitroxide and the phenolic antioxidant causing an increased consumption of the antioxidant.
Reactions between decomposition products of the phenolic antioxidant
TE D
•
(quinones) leading to deactivation of the nitroxide and acceleration of the decomposition of hydroperoxides by the salt of the HAS and the phenolic
EP
antioxidant [79.]
Dependent on the type of phosphite for combinations of HAS and phosphites, synergisms as well as antagonisms are reported [78,83].
AC C
Sulphur containing stabilizers are in use to increase the long-term heat stability of polymers. It was shown that HAS and sulphur containing stabilizers behave in many cases antagonistic [84], which was ascribed to the formation of a salt between acidic decomposition products of the –S- containing stabilizer and the basic HAS [85] or with the nitroxide itself [86,87]. It was shown that by applying less basic HAS derivatives the deactivation by a sulphur containing stabilizers can be reduced [88].
As many of the HAS stabilizers in use are basic, they will form salts when they are exposed to acids from the surrounding or from other additives as e.g. halogen containing
ACCEPTED MANUSCRIPT
flame retardants [89,90]. It was shown that the exposure of HAS to HCl, HBr and HNO3 had a large negative effect, sulphurous acid was somewhat less detrimental and formic acid, which is the strongest carboxylic acid that can be formed during the oxidation of polyolefins, had no effect [91].
RI PT
In the presence of halogenated flame retardants the activity of HAS is limited [90,92], which is ascribed to the formation of the ammonium salt of the HAS [89,93].
Another antagonistic effect reported is the interaction between agrochemicals and HAS, which caused a reduction of the effectivity of HAS as stabilizers for polymers applied in greenhouses [94]. It was shown that sulphur containing as well as acidic species from
HAS stabilizers were developed [88,97].
SC
pesticides and insecticides can be harmful [95,96].To reduce these problems less basic
M AN U
As mentioned above bridged amines show a synergism with HAS in preventing UVdegradation [98]. In reducing the thermo-oxidative degradation rate, aliphatic amines and HAS showed synergisms [98,99]. The aliphatic amine could be added separately or be a part of the chemical structure of the HAS (as e.g. in HAS-5). This stabilizing action of the aliphatic amine was ascribed to their ability to react with aldehydes and in this way prevent the formation of peracids.
References
TE D
7
1 F. Gugumus, in Oxidation Inhibition In Organic Materials,Vol. II, ed. J. Pospisil and P. P. Klemchuk. CRC Press, Boca Raton, FL, pp. 29-163. 2 H. Zweifel, R. Maier, M. Schiller, Plastics Additives Handbook 6th Edition, Munich: Hanser
EP
Publications; 2009.
3 R. Maier, M. Schiller, Handbuch Kunststoff Additive, Munich: Hanser Publications; 2016.
AC C
4 K. Murayama, T. Yoshioka, Stable free radicals. IV. Decomposition of stable nitroxide radicals, Bull Chem Soc Japan 42 (1969) 2307-2309. 5 T. Toda, T. Kurumada, K. Murayama, Progress in the light stabilization of polymers, Amer Chem Soc Symp Ser 280 (1985) 37-54. 6 P. Gijsman, M. Gitton, Hindered Amine Stabilisers as Long-term Heat Stabilisers for Polypropylene, Polym Degrad Stab 66 (1999) 365-371. 7 G. Balint, A. Rockenbauer, T. Kelen, F. Tudos, L. Jokay, Esr study of polypropylene photo stabilisation by sterically hindered piperidine derivatives, Polym Photochem 1 (1981) 139-152.
ACCEPTED MANUSCRIPT
8 D. K. Hodgeman, Formation of Polymer-Bonded Nitroxyl radicals in the UV Stabilization of Polypropylene by a Bifunctional Hindered Amine light Stabilizer, J Polym Sci Polym Chem Ed 19 (1981) 807-818. 9 J. Pilař, D. Michálková, I. Šeděnková, J. Pfleger, J. Pospíšil, NOR and nitroxide-based HAS in
RI PT
accelerated photooxidation of carbon-chain polymers; Comparison with secondary HAS: An ESRI and ATR FTIR study, Polymer Degradation and Stability 96 (5) (2011) 847-862.
10 J. Pilař, D. Michálková, M. Šlouf, T. Vacková, J. Dybal, Heterogeneity of accelerated
photooxidation in commodity polymers stabilized by HAS: ESRI, IR, and MH study, Polymer Degradation and Stability 103 (1) (2014) 11-25.
SC
11 Yu. B. Shilov, R.M. Battalova, E.T. Denisov, Regeneration of iminoxyl radical during polypropylene oxidation, Doklad Acad Nauk USSR 207 (1972) 388-389.
(1995) 87-189.
M AN U
12 J. Pospíšil, Aromatic and Heterocyclic Amines in Polymer Stabilization, Adv Polym Sci 124
13 J. Sedlar, J. Petruy, J. Pak, M. Navrati, Polymer photostabilization by HAS derivatives: the role of piperidine-hydroperoxide associates, Polymer 21 (1980) 5-7.
14 J. M. Bobbitt, C. Bruckner, N. Merbouh, Oxoammonium- and nitroxide-catalyzed oxidations of alcohols, Org Reactions 74 (2009) 103–424.
15 F. Gugumus, Current trends in mode of action of hindered amine light stabilizers, Polym Degrad Stab 40 (1993) 167-215.
TE D
16 D.J. Carlsson, K.H. Chan, D.M. Wiles, Polypropylene photostabilization by tetramethylpiperidine species. in "Photodegradation and Photostabilisation of Coatings" eds. Pappas, S.R., Winslow, F.H., American Chemical Society Symposium Series No. 151, 1981, pp. 51-63.
17 G. Geuskens, G. Nedelkos, The oxidation of hindered amine light stabilizers to nitroxyl
EP
radicals in solution and in polymer, Polym Degrad Stab 19 (1987) 365-378. 18. T. Toda, E. Mori, K. Murayama, Stable free radicals. IX. Peroxy acid oxidation of hindered
AC C
secondary amines to nitroxide radicals, Bull Chem Soc Jpn 45 (1972) 1904-1908. 19. B. Felder, R. Schumacher, F. Sitek, Hindered Amine Light Stabilizers, A mechanistic study. ACS Symp Ser 280 (1985) 69-90. 20. A. Zahradnickova, J. Sedlar D. Dastych, Peroxy acids in photo-oxidized polypropylene, Polym Deg Stab 32 (1991) 155-176. 21 P. Gijsman, New synergists for Hindered Amine Light Stabilizers, Polymer 43 (2002) 15731579. 22 G. Gryn’ova, K. U. Ingold, M. L. Coote, New Insights into the Mechanism of Amine/Nitroxide Cycling during the Hindered Amine Light Stabilizer Inhibited Oxidative Degradation of Polymers, J. Am. Chem. Soc. 134 (2012) 12979−12988.
ACCEPTED MANUSCRIPT
23 Yu. B. Shilov, E.T. Denisov, Mechanism of the inhibiting activity of iminoxyl radicals during oxidation of polypropylene and polyethylene, Vysokomol. Soyed. A 14 (10) (1974) 2313-2316. 24 T.A.B.M. Bolsman, A.P. Blok, T.H.G. Frijns, Mechanism of the catalytic inhibition of hydrocarbon autoxidation by secondary amines and nitroxides, Rec J Royal Neth Chem Soc 97
RI PT
(1978) 313-319.
25 P.P. Klemchuck, M.E. Gande, Stabilization mechanisms of hindered amines, Polymer Degradation and Stability 22(3) (1988) 241-274.
26 P.P. Klemchuck, M.E. Gande, Hindered Amine Mechanisms: Part III-Investigations using isotopic labelling, Polymer Degradation and Stability 27 (1) (1990) 65-74.
SC
27 E.N. Step, J. Turro, M.E. Gande, P.P. Klemchuck, Flash photolysis and time-resolved electron spin resonance studies triplet benzophenone quenching by hindered amine light stabilizers
Photobiool A: Chem. 74 (1993) 203-210.
M AN U
(HAS). A comparison of HAS amines and aminoethers and hydrogen atom donors, J. Photochem
28 E.N. Step, J. Turro, M.E. Gande, P.P. Klemchuck, Mechanism of Polymer Stabilization by Hindered-Amine Light stabilizers (HAS). Model Investigations of the Interaction of peroxy Radicals with HAS Amines and Amino Ethers, Macromolecules 27 (1994) 2529-2539. 29 D. W. Grattan, D. J. Carlsson, D. M. Wiles, Polyolefin photo-stabilisation mechanisms. Reaction of tetramethylpiperidine derivatives in model systems, Polym Degrad Stab 1 (1979) 6984.
TE D
30 V. Ya. Shlyapintokh, V. B. Ivanoc, Antioxidant action of sterically hindered amines and related compounds in Developments in Polymer Stabilisation Ed. G. Scott, Applied Science Publisher London, Vol. 5 (1982) 41-70.
31 A.L.J. Beckwith, V. W. Bowry, K. U. Ingold, Kinetics of Nitroxide Radical Trapping. 1. Solvent
EP
Effects, J. Am Chem Soc 114 (1992) 4983-4992. 32 V. W. Bowry, K. U. Ingold, Kinetics of Nitroxide Radical Trapping. 2. Structural Effects, J. Am Chem Soc 114 (1992) 4992-4996.
AC C
33 A. Garton, D.J. Carlsson, D.M. and Wiles, Polymer Oxidation and Secondary Cage Combination of Peroxyl Radicals, Makromol Chem 181 (1980), 1841-1846. 34 P. Richters, Initiation process in the oxidation of polypropylene, Macromolecules 3 (1970) 262264.
35 J.B. Knight, P.D. Calvert and N.C. Billingham, Localization of oxidation in polypropylene, Polymer 26 (1985), 1713-1718. 36 G.A. George, M. Celina, C. Lerf, G. Cash and D. Wendell, A spreading model for the oxidation of polypropylene, Macromol Symp 115 (1997) 68–92. 37 M. Celina and G.A. George, Heterogeneous and homogeneous kinetic analysis of the thermal oxidation of polypropylene, Polym Degrad Stab 50 (1995) 89–99.
ACCEPTED MANUSCRIPT
38 I. Blakey and G.A. George, Raman spectral mapping of photo/oxidised polypropylene, Polym Degrad Stab 70 (2000) 269–275. 39 G. Ahlblad, P. Gijsman, B. Terselius, A. Jansson and K. Möller, Thermo-oxidative stablility of PP waste films as studied by imaging chemiluminescence, Polym Degrad Stab 73 (2001) 15–22.
RI PT
40 A.A. Oswald, F. Noel, A.J. Stephenson, Organic sulfur compounds. V. Alkylammonium thiolate and peroxide salts; possible intermediates in amine-catalyzed oxidation of mercaptans by hydroperoxides, J Org Chem 26 (1961) 3969-3974.
41 D.W. Grattan, A.H. Reddoch, D.J. Carlsson, D.M. Wiles, Polymer photostabilization by
piperidine derivatives: the role of nitroxide-hydroperoxide complexing, J Polym Sci: Polym Lett
SC
Ed 16 (1978) 143-148.
42 F. Gugumus. Developments in the U.V.-stabilisation of polymers,in Developments in Polymer Stabilisation Ed. G. Scott, Applied Science Publisher London, Vol. 1 (1979) 261-308.
M AN U
43 M. G. Chan, Metal deactivators, in Oxidation Inhibition in Organic Materials Vol 1 Eds J. Pospisil, P. P. Klemchuck, CRC Press Inc Boca Raton, Florida (1990) pp. 225-246. 44 S.P. Fairgrieve, J.R. Mac Callum, Photostabilization by hindered amines: the role of transition metal complexation, Polymer Communications 25 (2) (1984) 44-6.
45 S.P. Fairgrieve, J.R. Mac Callum, Hindered Amine Light Stabilizers: A proposed photostabilization mechanism, Polym Degrad Stab 8 (1984) 107-121.
46 J. Sedlar, J. Petruj, J. Pac, A. Zahradnicova, Photostabilizing action of sterically hindered
662.
TE D
piperidines-1, peroxide decomposing and hydrogen donating ability, Eur. Polym J 16 (1980) 659-
47 F. Gugumus, Findings pertaining to polyethylene photooxidation, Makromol. Chem. Macromol. Symp. 25 (1989) 1-22.
48 P. Gijsman, J. Hennekens and D. Tummers, The mechanism of action of hindered amine light
EP
stabilizers, Polym Degrad Stab 39 (1993) 225–233. 49 P. Gijsman, A. Dozeman, Comparison of the UV-degradation chemistry of unstabilized and
AC C
HAS-stabilized polyethylene and polypropylene, Polym Degrad Stab 53 (1996) 45-50. 50 Th. Schmutz, E. Kramer, H. Zweifel, G. Dorner, Advanced extraction resistant long-term thermal stabilizers for polyolefin pipes, Journal of Elastomers and Plastics 30 (1) (1998) 55-67. 51 V. Malatesta, L. Davis, J. Zenner, High heat and UV-stabilization of polyolefins under demanding conditions. Addcon World 2005, International Conference, 11th, Hamburg, Germany, Sept. 21-22, 2005 (2005) Paper 7/1-Paper 7/11. 52 C.M. Liauw, A. Quadir, N.S. Allen, M. Edge, A. Wagner, Effect of hindered piperidine light stabilizer molecular structure and UV-absorber addition on the oxidation of HDPE. Part 1: Longterm thermal and photo-oxidation studies, Journal of Vinyl & Additive Technology 10 (2) (2004) 79-87.
ACCEPTED MANUSCRIPT
53 F. Gugumus, Advances in the stabilization of polyolefins. Polymer Degradation and Stability 24 (4) (1989) 289-301. 54 F. Gugumus, Mechanisms of thermooxidative stabilization with HAS, Polym. Degrad Stab. 44 (1994) 299–322.
Polymers, Luzern (1992), Proceedings pp 57.
RI PT
55 W.O. Drake, Fourteenth International Conference on the Stabilization and Degradation of
56 P. Gijsman, H.J. Smelt, D. Schumann, Hindered amine light stabilizers: An alternative for radiation cross-linked UHMwPE implants, Biomaterials 31 (26) (2010) 6685-6691.
stabilizers, Polym. Deg. Stab. 43 (1994) 171-176.
SC
57 P. Gijsman, The mechanism of action of hindered amine stabilizers (HAS) as long-term heat
58 W.W. Müller, I. Jakob, R. Tatzky-Gerth, A. Wöhlecke, A study on antioxidant depletion and
Eng Sci 56 (2016) 129–142.
M AN U
degradation in polyolefin-based geosynthetics: Sacrificial versus regenerative stabilization. Polym
59 P. Gijsman, J. Hennekens and J. Vincent, The mechanism of the low temperature oxidation of polypropylene, Polym. Deg. Stab. 42 (1993) 95-105.
60 N.C. Billingham, Localization of oxidation in polypropylene, Makromol Chem Macromol Symp 28 (1989) 145-163.
61 I. Blakey, N.C. Billingham, G.A. George, Use of 9,10-diphenylanthracene as a contrast agent in chemiluminescence imaging: The observation of spreading of oxidative degradation in thin
TE D
polypropylene films, Polymer Degradation and Stability 92(11) (2007) 2102-2109. 62 P. Eriksson, T. Reitberger, B. Stenberg, Gasphase distribution to the spreading of oxidation in PP as studied by imaging Chemiluminescence, Polym. Degrad. Stab. 78 (2002) 183-189. 63 M. Celina, R.L. Clough, G.D. Jones, Initiation of polymer degradation via transfer of infectious species, Polym. Degrad. Stab 91 (2006) 1036-1044.
EP
64 M. Hamskog, B. Terselius, P. Gijsman, Mapping of heterogeneous degradation of polypropylene using Imaging Chemiluminescence, Polym. Deg. Stab. 82 (2003) 181-186.
AC C
65 P. Gijsman, Mechanism of the thermo-oxidative degradation of unstabilized, phenolic antioxidant and hindered amine stabilizer containing polypropylene” in “Specialty Polymer Additives” eds S. Al-Malaika, A. Golovoy, C.A. Wilkie, Blackwell Science, Oxford, 2001 pp 67-90. 66 J. Pospisil, W.-D Habicher, J. Pilar, S. Nespurek, J. Kuthan, G-O Piringer, H. Zweifel, Discoloration of polymers by phenolic antioxidants, Polymer Degradation and Stability 77 (3) (2002) 531-538.
67 R.V. Todesco, R. Diemunsch, T. Franz, New developments in the stabilization of PP fibers for automotive applications Chemiefasern/Textilindustrie, 43 (10) (1993), E135-E137, T197-T199. 68 P. Solera, New trends in polymer stabilization, Journal of Vinyl & Additive Technology 4 (3) (1998) 197-210.
ACCEPTED MANUSCRIPT
69 E. Oral, C. Godleski Beckos, A.S. Malhi, O.K. Muratoglu. The effects of high dose irradiation on the cross-linking of vitamin E-blended ultrahigh molecular weight polyethylene, Biomaterials 29 (2008) 3557-60. 70 M. Parth, N. Aust, K. Lederer, Studies on the effect of electron beam radiation on the
RI PT
molecular structure of ultra-high molecular weight polyethylene under the influence of alphatocopherol with respect to its application in medical implants. Journal of Materials Science: Materials in Medicine 13 (2002) 917-21.
71 E. Oral, E.S. Greenbaum, A.S. Malhi, W.H. Harris, O.K. Muratoglu, Characterization of irradiated blends of alpha-tocopherol and UHMWPE, Biomaterials 26 (2005) 6657-63.
SC
72 P. Delprat, X. Duteurtre, J-L. Gardette, Photo-oxidation of unstabilized and HALS-stabilized polyphasic ethylene-propylene polymers, Polym Degrad Stab 50 (1995) 1-12.
Stability 44 (3) (1994) 273-97.
M AN U
73 F. Gugumus, New trends in the stabilization of polyolefin fibers, Polymer Degradation and
74 F. Gugumus, Possibilities and limits of synergism with light stabilizers in polyolefins 1. HALS in polyolefins, Polymer Degradation and Stability 75(2) (2002) 295-308.
75 N.S. Allen, J.F. McKellar, Photostabilization of commercial polypropylene by hindered piperidine compounds, Plast Rubber Mat Applicat, Nov 1979 170-174. 76 N.S. Allen, Photo-stabilising performance of a hindered piperidine compound in polypropylene film: anti-oxidant/light stabiliser effects, Polym Degrad Stab 2 (1980) 129-135.
TE D
77 J. Lucki, J.F. Rabek, B Ranby, Photostabilizing Effect of Hindered Piperidine Compounds: lnteraction Between Hindered Phenols and Hindered Piperidines, Polym Photochem 5 (1984) 351-354.
78 N.S. Allen, A. Hamid, F.L. Loffelman, P. Macdonald, M. Rauhut, P.V. Sushi, Interactions of antioxidants with hals in the thermal and photochemical oxidation of pp film, Plast Rubber
EP
Process Applicat 5 (1985) 259-265.
79 H. Yamashita, Y. Ohkatsu, A new antagonism between hindered amine light stabilizers and
AC C
acidic compounds including phenolic antioxidants, Polym Degrad Stab 80 (2003) 421–426. 80 J E. Volponi, L.H.I. Mei, D. dos Santos Rosa, The use of differential photocalorimetry to measure the oxidation induction time of isotatic polypropylene, Polymer Testing 23 (2004) 461465.
81 P. Gijsman, J. Sampers, W. Bunge, J. Vaassen, Stabilized polypropylene resin composition, EP1340789.
82 L. Maringer, L. Roiser, G. Wallner, N. Gernot, D. Nitsche, W. Buchberger, The role of quinoid derivatives in the UV-initiated synergistic interaction mechanism of HALS and phenolic antioxidants, Polymer Degradation and Stability 131 (2016) 91-97.
ACCEPTED MANUSCRIPT
83 I. Bauer, W.D. Habicher, S. Korner, S. Al-Malaika, Antioxidant interaction between organic phosphites and hindered amine light stabilizers: effects during photoxidation of polypropylene-II, Polym Degrad Stab 55 (1997) 217-224. 84 S. W. Bigger, O Delatycki, The effect of hindered amine light stabilizers on the photoxidative
RI PT
stability of high density polyethylene, J Polym Sci A Polym Chem 27 (1989) 63-73.
85 L. Yu. Smoliak, N. R. Prokopchuck, Y. P. Losev, V. P. Prokopovich, I. A. Klimotsova,The role of sulphur containing groups in inhibition of oxidative degradation of polyolefins by HALS, Polym Blends Polym Composit 1 (2002) 151-159.
86 K. Kikkawa, Y. Nakahara, Antagonism between hindered amine light stabilizers and sulphur-
SC
containing compounds, Polym Degrad Stab 18 (1987) 237-245.
87 J. Lucki, S. Z. Jian, J. F. Rabek, B. Ranby, Antagonistic Effects of Hindered Piperidines and
27-47.
M AN U
Organic Sulphides in Photostabilization of cis –1,4- Polybutadiene, Polym Photochem 7 (1986)
88 R.L. Gray, Additives: a novel non reactive HALS Boosts polyolefin stability, Plast Eng 47 (6) (1991) 21-23.
89 J-L. Gardette, C. Sinturel, J. Lemaire, Photooxidation of fire retarded polypropylene, Polym Degrad Stab 64 (1999) 411-417.
90 K. Antos, J. Sedlar, Influence of brominated flame retardant thermal decomposition products on HALS, Polym Degrad Stab 90 (2005) 188-194.
TE D
91 D.J. Carlsson, K. Zhang, D.M. Wiles, Polypropylene Photostabilization by Hindered Amines in the Presence of Acidic Species J Appl Polym Sci 33 (1987) 875-884. 92 R.L. Gray, R.E. Lee, UV stabilization of polypropylene fiber containing organic bromine flame th
retardants Annual Technical Conference - Society of Plastics Engineers 54 (Vol 3) (1996), 30283032.
EP
93 C. Sinturel, J. Lemaire, J-L Gardette, Photooxidation of fire retarded polypropylene. III. Mechanism of HAS inactivation, European Polymer Journal 36 (7) (2000) 1431-1443.
AC C
94 J.H. Khan, S.H. Hamid, Durability of HALS-stabilized polyethylene film in a greenhouse environment, Polym Deqrad Stab 48 (1995) 137-142. 95 E. Epacher, B, Pukanszky, Interactions of pesticides and stabilizers in PE films for agricultural use, Antec (1999) 3785-3790. 96 J-R. Pauquet, Technological advances in the stabilization of polyethylene films, Plast Rubber Composit Process Applications 27 (1998) 19-24. 97 P. Solera, G. Capocci, Designing higher performance: A new light stabilizer for polyolefins Polyolefins 2000, International Conference on Polyolefins, Houston, TX, United States, Feb. 27Mar. 1, 2000 (2000), 699-713.
ACCEPTED MANUSCRIPT
98 P. Gijsman. M. Gitton, Aliphatic Amines for use as Long-term Heat Stabilisers for Polypropylene, Polym. Deg. Stab. 81 (2003) 483-489. 99 A. Rosales Jasso, M.L. Berlanga Duarte, N.S. Allen. Synergistic Effect between Hindered
AC C
EP
TE D
M AN U
SC
Applied Polymer Science 92 (2004) 280–287.
RI PT
Amine Light Stabilizers and Partially Hindered Oligomeric Amines in Polyethylene, Journal of
ACCEPTED MANUSCRIPT
8
Appendix
Abbreviation Chemical structure
Trade name(s) ( Supplier)
RI PT
Anox® PP18 (Addivant) Irganox® 1076 (BASF)
AO-1
Songnox® 1076 (Songwon) Thanox® 1076 (Rianlon)
SC
Irganox® E201 (BASF)
AO-2
Quali®-E (DSM)
N H
HAS-1
M AN U
Lowillite® 77 (Addivant)
O
O
O
O
Sabo® stab UV 70 Songlight® 7700 (Songwon) Tinuvin® 770 (BASF)
H N
AC C
HAS-3
EP
HAS-2
TE D
Chimassorb® 944 (BASF) Lowilite® 94 (Addivant) Sabo® stab UV 944 (Sabo) Songlight® 9440 (Songwong)
BLS® 123 (Mayzo) Milestab® 123 (MPI Chemie) Omnistab® LS 123 (Deltachem (QingDao) Tinuvin® 123 (BASF)
ACCEPTED MANUSCRIPT
Abbreviation Chemical structure
Trade name(s) ( Supplier) CH3 N
Lowilite 92 (Addivant) O
HAS-4
O O
Milestab® 765 (MPI Chemie) Sabo® Stab UV 65 (Sabo)
RI PT
O
CH3 R R
HN NH
R N N
Lowilite® 19 (Addivant)
R
Sabo® stab UV 119 (Sabo)
C4H9
R=
N N
M AN U
HAS-5
Songlight® 1190 (Songwong)
N N
N
N C4H9 N
CH3
EP
TE D
CH3
AC C
SC
Tinuvin® 765 (BASF) N