Benzotriazole-antioxidant

Figure 10. Inhibition of discoloration with benzotriazole-antioxidant...

As already shown, it is technically possible to incorporate additive functional groups within the structure of a polymer itself, thus dispensing with easily extractable small-molecular additives. However, the various attempts of incorporation of additive functionalities into the polymer chain, by copolymerisation or free radical initiated grafting, have not yet led to widespread practical use, mainly for economical reasons. Many macromolecular stabiliser-functionalised systems and reactive stabiliser-functionalised monomers have been described (cf. ref. [576]). Examples are bound-in chromophores, e.g. the benzotriazole moiety incorporated into polymers [577,578], but also copolymerisation with special monomers containing an inhibitor structural unit, leading to the incorporation of the antioxidant into the polymer chain. Copolymers of styrene and benzophenone-type UV stabilisers have been described [579]. Chemical combination of an antioxidant with the polymer leads to a high degree of resistance to (oil) extraction. 

FD-MS is also an effective analytical method for direct analysis of many rubber and plastic additives. Lattimer and Welch [113,114] showed that FD-MS gives excellent molecular ion spectra for a variety of polymer additives, including rubber accelerators (dithiocar-bamates, guanidines, benzothiazyl, and thiuram derivatives), antioxidants (hindered phenols, aromatic amines), p-phcnylenediamine-based antiozonants, processing oils and phthalate plasticisers. Alkylphenol ethoxylate surfactants have been characterised by FD-MS [115]. Jack-son et al. [116] analysed some plastic additives (hindered phenol AOs and benzotriazole UVA) by FD-MS. Reaction products of a p-phenylenediaminc antiozonant and d.v-9-lricoscnc (a model olefin) were assessed by FD-MS [117],... 

Meyer-Dulheuer [55] has analysed the pure additives (phenolic antioxidants, benzotriazole UV stabilisers and HALS compounds) of Table 9.8 in THF solutions by means of MALDI-ToFMS. As it turns out, polar molecules in the mass range of below 800 Da, which have a high absorption coefficient at the laser wavelength used, can often be measured without any matrix [55,56]. In this case, there is no matrix-assisted laser desorption and ionisation (MALDI) process any more. It is a simple laser desorption/ionisation (LDI) process. The advantage of this method is a matrix-free mass spectrum with the same mass resolution as in the MALDI case,... 

Polystyrene light stabilization has been achieved with a variety of ulfravioler absorbers including the benzophenones, benzotriazoles. and salicylates. While yellowing of polystyrene occurs in many applications, it is particularly noticeable in diffusers used with fluorescent lights. This problem has been effectively solved by using ultraviolet light absorbers. In this instance, superior stabilization is achieved when the ultraviolet absorber is used in conjunction wirh specific antioxidants. 

The stabilizers chosen for evaluation include different types of heat and light stabilizers selected to represent different mechanisms of action as well as chemical compositions (ArJi). Types of stabilizers evaluated include benzotriazole and benzophenone light stabilizers [ultraviolet (UV) light absorbers], hindered amine light stabilizers (HALS, catalytic radical scavengers), hindered phenol heat stabilizers (antioxidant radical scavengers), and thioester heat stabilizers (antioxidant hydroperoxide decomposers). 

Four main types of antioxidants are commonly used in polypropylene stabilizer systems although many other types of chemical compounds have been suggested. These types include hindered phenolics, thiodi-propionate esters, aryl phosphites, and ultraviolet absorbers such as the hydroxybenzophenones and benzotriazoles. Other chemicals which have been reported include aromatic amines such as p-phenylenediamine, hydrocarbon borates, aminophenols, Zn and other metal dithiocarbamates, thiophosphates, and thiophosphites, mercaptals, chromium salt complexes, tin-sulfur compounds, triazoles, silicone polymers, carbon black, nickel phenolates, thiurams, oxamides, metal stearates, Cu, Zn, Cd, and Pb salts of benzimidazoles, succinic acid anhydride, and others. The polymeric phenolic phosphites described here are another type. 

Further examples reported in Table 40 arc given by the alkyl ketone moieties deriving from oxidation of polyenes, which arc subjected to Mannich aminomethylation in order to produce compounds 559 having dispersant properties for lubricating oils, by benzotriazoles 557, capable of forming, due to physical adsorption, thin layers over the surfaces subjected to friction, and by S-Mannich bases 558, combining antifriction and antioxidant properties. 

Features of the free-radical initiation processes are similar for both the homopolymerization of functionalized monomers and copolymerization of the latter with conventional monomers. Common chemical initiators were applied. Azo-bis(isobutyro nitrile) was mostly used in bulk polymerization. No interference with phenolic hydroxy groups was observed in polymerization of 2-hydroxybenzo-phenoiKs, acetophenones, salicylates and of their derivatives [47]. The most rigorous eliinination of oxygen from the reaction mixture was necessary to achieve polymerization of monomeric hindered phenolic antioxidants or derivatives of 2-(2-hydroxyphenyl)benzotriazole [48]. An oxygen-free atmosphere is also an advantage for aromatic amines. A higher initiator level and/or increased temperature appear to be necessary to achieve normal polymerization rates with (D-functionalized monomers [46]. 

The variety of substances used as additives in polymers is considerable. For example, the fillers may include china clay, various forms of calcium carbonate, talc, silicas (diatomaceous silica), silicates, carbon black, etc. The impact modifiers typically include other polymers. Plasticizers include certain polymers with low (oligomers), dialkyl phthalates, dialkyl sebacates, chlorinated paraffin waxes, liquid paraffinic fractions, oil extracts, etc. Heat stabilizers include heavy metals salts such as basic lead carbonate, basic lead sulfate, dibasic lead phosphite (also acting as a light stabilizer), dibasic lead phthalate, stearates, ricinoleates, palmitates and octanoates of cadmium and barium, epoxide resins and oils, amines, diphenylurea, 2-phenylindole, aminocrotonates. The antioxidants include tris-nonyl phenyl phosphite, 2,6-di-ferf-butyl-p-cresol (BHT), octadecyl-3,5-di-terf-butyl-4-hydroxyhydrocinnamate, etc. The UV stabilizers include modified benzophenones and benzotriazoles. Processing lubricants include calcium stearate, stearic acid, lead stearate, various wax derivatives, glyceryl esters and long-chain acids. Fire retardants include antimony oxide, some pyrophosphates, etc. 

Suggestions have also been made that better overall performance can be achieved by the use of more than one benzophenone [37], or combinations with other classes of stabiliser such as benzotriazoles or cinnamates [36], or in combination with antioxidants [41, 42]. 

Additive packages containing benzotriazoles along with other co-additives are also known. These include combinations with benzophenones and/or cinnamate-types [36] with antioxidants [41, 42] with fatty acid salts of manganese [55] combinations of polyoxyalkyene-based benzotriazoles and PEN used in PET [61] and benzotriazole plus poly(isobornyl acrylate) for the protection of polyalkylene naphthalates [62]. 

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