Michael M. Rauhut

STRUCTURAL CRITERIA FOR CHEMILUMINESCENCE IN ACYL PEROXIDE DECOMPOSITION REACTIONS

Abstract— A group of new moderately bright chemiluminescent reactions is reported involving decomposition of certain acyl peroxide derivatives. The new chemilurninescent reactions are compared to other acyl peroxide decompositions which are not strongly chemiluminescent (Chart I). The results are interpreted in terms of a concerted multiple bond cleavage peroxide decomposition mechanism, where the simultaneous formation of at least two stable molecules is suggested to be the source of the substantial energy required for the formation of an excited reaction product in chernilurninescence.

Photo-stabilising action of a p-hydroxybenzoate light stabiliser in polyolefins: Part III—Antioxidant behaviour and additive/pigment interactions in high density polyethylene

Abstract The effect of a number of commercial primary and secondary antioxidants, light stabilisers and pigments on the photo-stabilising action of an n -alkyl substituted p -hydroxybenzoate light stabiliser (Cyasorb® UV 2908) is examined in high density polyethylene. At the concentration levels employed here the p -hydroxybenzoate light stabiliser showed a favourable interaction with all the light stabilisers and pigments studied. Interactions with the primary and secondary antioxidants appeared to be concentration dependent. Synergism with the light stabilisers is associated with the ability of these compounds to destroy hydroperoxides and/or react with alkoxy and hydroxy radicals produced in their photolysis. Synergism with primary and secondary antioxidants is observed at low concentrations of each component (0·05% w/w each) whereas antagonism is observed at higher concentration levels, the latter being associated with unfavourable interactions between intermediate radical products of the additives. With the pigments there is strong synergism and this is associated with the known ability of the pigments to catalyse the photo-decomposition of hydroxperoxides, the resulting alkoxy and hydroxyl radicals being effectively scavenged by the p -hydroxybenzoate stabiliser. Further information on the selectivity of the p -hydroxybenzoate light stabiliser to terminate only the active free radical species in the polymer compared with conventional antioxidant structures is also provided.

Spectroscopic properties and mechanistic action of a new p-hydroxybenzoate light stabiliser: a comparative study in polypropylene and high density polyethylene and anti-oxidant interactions

The photostabilising action of an n-alkyl substituted p-hydroxybenzoate light stabiliser (Cyasorb® UV 2908) is examined in both polypropylene and high density polyethylene using luminescence, normal and derivative uv-visible and infra-red spectrophotometric techniques and hydroperoxide analysis. By comparison with various anti-oxidants it proved to be a very effective light stabiliser in high density polyethylene but not in polypropylene. Whilst its uv absorption spectrum showed it to be a non-absorber in sunlight its luminescence properties were totally different from those of conventional anti-oxidant structures. The photostabilising action of the p-hydroxybenzoate light stabiliser is found to be dependent on the initial concentration of hydroperoxide groups in the polymer indicating that it is an effective alkoxy and hydroxy radical scavenger. In polypropylene, it suppressed hydroperoxide formation during processing but had no effect in high density polyethylene, indicating it to be an effective thermal anti-oxidant in the former polymer. Using methylene blue as a singlet oxygen sensitiser and dimethylanthracene as a chemical trap, the stabiliser proved ineffective in quenching singlet oxygen in the polymer matrix. Its inability to photolyse to give active quinone products, good compatibility and alkoxy and hydroxy radical terminating properties are concluded to be key factors responsible for its light stabilising function in high density polyethylene. The interaction of the light stabiliser with conventional thermal primary anti-oxidants is also examined and discussed.

Photostabilising action of a p-hydroxybenzoate light stabiliser in polyolefins: Part IV—Catalyst effects and additive interactions in linear low density polyethylene

Abstract The photostabilising action of a p -hydroxybenzoate light stabiliser (Cyasorb® UV2908) is examined in linear low density polyethylene (LLDPE). The efficiency of this light stabiliser is shown to be significantly influenced by levels of residual catalyst such as Ti and Al. Deactivation of the catalysts with phosphoric acid in 2-propanol markedly improves both the performance and light stability of the stabiliser. Processing history reduces the efficiency of the stabiliser whereas its light stability increases linearly with processing time and is associated with the ability of the residual catalyst to destroy hydroperoxides during processing. Stabilising efficiency, however, is reduced by a corresponding reduction in stabiliser concentration during processing. The stabiliser synergises effectively during both oven ageing and photo-oxidation with a hindered piperidine light stabiliser due to the complementary function of each additive. Thus, whilst the former terminates primarily alkoxy/hydroxy radicals produced from the decomposition of hydroperoxides, the latter destroys hydroperoxides in a stoichiometric reaction and through the nitroxyl radical intermediate which selectively reacts with macroalkyl (P • ) radicals and through the hydroxylamine which reacts with peroxy radicals (PO 2 • ). Strong synergism is also observed with TiO 2 (rutile).

Chemical Light Product Research and Development

Chemiluminescence research was initiated in the Author’s laboratory in 1961 with the objective of developing efficient chemical lighting systems for use in practical lighting applications. The preliminary phase of the program consisted of market research, feasibility analysis and selection of an optimum research approach.