SECONDARY STABILISER

Many industrial laboratories conducting significant amounts of additive analyses have developed a universal HPLC method which may be used to separate most of the additives of interest. Thomas [417] has reported a method that can separate over 20 common primary and secondary stabilisers. Verdurmen et al. [197] employ a gradient ranging from 60 % acetonitrile/40 % water to 100% acetonitrile subsequently, all components are eluted off the column in isocratic mode. Irganox 1063 is used as a suitable internal standard since this compound is not frequently encountered in commercial polymers, elutes without overlap to other additives and shows good UV absorbency. In order... 

Recent investigations covering S-PVC polymerisation are to be found in (35,166,318,345,429). Topics cover improved reactor economics, polymerisation in the presence of calcium carbonate, secondary stabilisers to impart higher grain porosity to assist in improving VCM removal and plasticiser uptake, initiator stabilisers and an investigation on the effects of polymerisation conditions on PVC particles. 

An additive system was developed for poly(vinyl chloride) for medical applications. The additives include primary stabilisers (Ca-Zn stearate and Zn stearate), secondary stabilisers (epoxides) and lubricants (ethylene bisamide and high density polyethylene), to improve melt processing and heat stability. The use of the stabilisers resulted in reduced equipment down-time, increased the level of recycled material which could be incorporated, and enhanced the product characteristics, including colour, clarity, blush, aqueous extractables and particle generation. 5 refs. 

Brighton, 20th-22nd April 1999, p.451-8 WATER DILUTABLE SECONDARY STABILISERS IN THE SUSPENSION POLYMERISATION OF PVC Prince K D... 

Organotin stabilisers have a strong affinity for PVC, attaching themselves to the chlorine atoms on the outer surfaces of primary polymer particles. They act as primary stabilisers insofar as they are involved with the substitution of the allylic chlorine atoms, and they react with hydrogen chloride to form alkyl thioglycolates that, once produced, act as secondary stabilisers. 

Nevertheless, Greenpeace frequently draws the attention of the public to its concerns about tin in PVC. The toxicity of organotin compounds varies considerably dibutyl tin chloride has one of the lowest oral LD50 values, although others are eye irritants. Dover Chemical has suggested that Doverlube TriCal, its new calcium stearate product, can be used as a secondary stabiliser to reduce the amoimt of tin needed. 

Thermogravimetry coupled with FTIR was used to investigate the stabilising action of 3-(2,4-dibromophenylazo)-9-(2,3-epoxypropane)carbazole on the degradation of PVC. This secondary stabiliser increased the initial temperature of hydrogen chloride evolution (the main process responsible for PVC decomposition), thereby allowing its application for novel PVC systems with enhanced thermal stability. 10 refs. EASTERN EUROPE POLAND Accession no. 731454... 

The excess of acid (0-5-1 equivalents) maintains a proper condition of acidity required to stabilise the diazonium salt solution by reducing the secondary... 

Discussion of ketone oxidation has centred around the identity of the molecule undergoing oxidation. This has been clearly resolved in some, but not all, cases, the evidence resting on (i), the relative rates of enolisation and oxidation, (ii) kinetic orders and (ih) isotope effects. A general feature of the oxidations of ketones by one-equivalent reagents is that the rate for a given oxidant exceeds that for oxidation of a secondary alcohol by the same oxidant. The most attractive explanation is that the radical formed from a ketone is stabilised by delocalisation, viz. 

Kellum [115] has described a class-selective oxidation chemistry procedure for the quantitative determination of secondary antioxidants in extracts of PE and PP with great precision (better than 1 %). Diorgano sulfides and tertiary phosphites can be quantitatively oxidised with /-chloropcroxybenzoic acid to the corresponding sulfones and phosphates with no interference from other stabilisers or additives. Hindered phenols, benzophenones, triazoles, fatty acid amides, and stearate... 

Wieboldt et al. [560] have described SFE-SFC-FTIR analysis of hindered phenol primary antioxidants and phosphite secondary antioxidants in PE. SFE is more selective for the lower-range low-MW polymer than Soxhlet-type extraction. This yields a chromatogram with less interference from low-MW polymer peaks in the region where the additive components elute. As a result, SFE appears to be a better choice than Soxhlet-type extraction for the selective removal of additives from flaked polymer. SFE and dissolution/precipitation methods were compared for a PVC/stabiliser system [366]. 

Despite the fact that the exo adduct is likely to be the more stable of the two thermodynamically, it is often (though not universally) found in Diels-Alder reactions that the endo adduct is the major, if not the sole, product. To explain this, it has been suggested that in endo addition stabilisation of the T.S. can occur (and the rate of reaction thereby speeds up) through secondary interaction of those lobes of the HOMO in, e.g. (32) and of the LUMO in (33) that are not themselves involved directly in bond-formation, provided these are of the same phase. Such interaction would not, of course, be possible in the T.S. for exo addition because the relevant sets of centres in (32) and (33) will now be too far apart from each other the endo adduct is thus the kinetically controlled product. It is significant in this connection that the relative proportion of exo... 

Ejection of dinitrogen from the triazoline adducts to form the related aziridines was promoted by ultraviolet irradiation (300 nm, benzene) and usually proceeded in excellent yield. An exception was found in the irradiation of the triazoline substrate 59, where cleavage of the cyclobutane ring occurred as the dominant reaction pathway to form the pyridazino norbomadiene 61 (and secondary photoproducts derived therefrom), together with the triazole-4,5-diester 62. A role for the pyridazine ring and the 2-pyridyl substituents in stabilising the diradical intermediate 60 has been proposed for this abnormal outcome (Scheme 8). 

Superior passive stabilised diazo compounds are afforded by the diazoamino compounds (triazenes) that arise by reaction of diazonium salts with a variety of secondary amines [114]. Typically, sarcosine (CH3NHCH2COOH), which gives products based on structure 4.114, as well as N-methyltaurine (CH3NHCH2CH2SO3H) and N methylaniline-4 Sulphonic acid,... 

This means that the isopropyl group stabilises the secondary ion sufficiently (compared to but-l-ene) for hydride transfer reactions to be suppressed, at least at low temperature. At about -120 °C a high polymer of structure (IV) is formed. This is a true phantom polymer, since there exists no corresponding monomer. Evidently, at the very low temperature the propagation reaction which would lead to structure (III) becomes much slower than the isomerization reaction ... 

Antioxidants act so as to interrupt this chain reaction. Primary antioxidants, such as hindered phenol type antioxidants, function by reacting with free radical sites on the polymer chain. The free radical source is reduced because the reactive chain radical is eliminated and the antioxidant radical produced is stabilised by internal resonance. Secondary antioxidants decompose the hydroperoxide into harmless non-radical products. Where acidic decomposition products can themselves promote degradation, acid scavengers function by deactivating them. 

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