Organo-cuivreux vinyliques 171. Carbocupration d'alcynes par des organo-cuprates et -cuivreux fonctionnels

Some organocopper and cuprate derivatives, distally bearing a free or protected hydroxyl group, add to alkynes, to give α,ω-bifunctional olefins.     

Direct sample fraction deposition using electrospray in narrow-bore size-exclusion chromatography/matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for polymer characterization

A direct sample fraction deposition method was developed for off-line size-exclusion chromatography (SEC)/matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry. By using electrospray, the SEC eluent, together with a suitable matrix solution added coaxially, was directly deposited on the MALDI plate. Owing to the formation of very small droplets in electrospray, solvent evaporation is much faster. The fractionation volume in narrow-bore SEC, which can directly be collected in one MALDI spot, can easily be optimized in the range of a few microlitres. In addition, fairly homogeneous sample spots were obtained. The possible influence of composition variation of the SEC effluent on the analytical results using direct fraction deposition was investigated; no substantial effects were observed. The applicability of the method was demonstrated by characterizing a broad poly(methyl methacrylate) sample. Copyright 2000 John Wiley & Sons, Ltd.     

Stabiliser interactions with hindered piperidine compounds in polypropylene: Influence of processing

The effect of two hindered piperidine compounds on the photo-stability and light stabilising performance of a 2-hydroxy-benzophenone and a 2-hydroxybenzotriazole stabiliser in polypropylene film has been examined. The piperidine compounds—a stable N-oxy radical and a hindered amine—inhibit the photolysis of both the benzophenone and the benzotriazole stabilisers, the amine being more effective. Processing reduces the protective efficiency of the piperidine compounds. The light stability of the polymer was, however, variable, both antagonism and synergism being observed. The processing operation had a dramatic effect on the light stabilising performance of the hindered amine systems whereas it had virtually no effect on the performance of the N-oxy radical systems. The inhibition process is attributed to a regeneration process involving the N-oxy radical and the effects of processing are attributed to the formation of hydroperoxides.     

Influence of water on the photodegradation of poly(ethylene oxide)

The UV-light degradation of polyethylene oxide (PEO) in aqueous solution was investigated operating under long wavelengths (λ > 300 nm) at 20 °C in different pH conditions varying from 2.3 to 12.0 and at two different concentrations. Thermo-oxidation experiments on PEO aqueous solution at 50 °C are also reported and compared to photo-oxidation results. The formation of oxidation products was followed by infrared analysis of deposits obtained by evaporation of aliquots of irradiated polymer solution. Photo-oxidation led to formates and esters but a third product was also identified, formic acid ions formed by partial hydrolysis of formates. The degradation of PEO in water led to the acidification of the aquatic medium. Size exclusion chromatography (SEC) was used to monitor the changes in molar weight and intrinsic viscosity with irradiation time. It was shown that the photo-oxidation produced a dramatic decrease of the average molar weights which is more important in acidic medium. Total organic carbon (TOC) measurements of the aged aqueous solutions showed that the mineralization of PEO could not be achieved in these photo-oxidative conditions.     

Basic Aspects of Polymer Degradation

Knowledge on the mechanisms by which polymers degrade on exposure to natural or artificial ageing has considerably increased during the past few years. One reason for this is the development of novel experimental procedures and analytical techniques. The analyses of the chemical changes permit determining the main degradation routes applicable to the degradation of the properties of materials and ensures the relevance of the laboratory experiments.     

Photooxidation of copolymers of fluorinated olefins and allyl or vinyl ethers

This article reports the results on the photooxidation mechanisms of two copolymers of fluorinated olefins and allyl or vinyl ethers. It is shown that the presence of the fluorine atoms influences strongly both the orientation of the reaction and the photooxidation kinetics. Due to the neighbouring fluorine atoms, the methylene groups in α-position of the oxygen of the ether groups are not equivalent regarding oxidation and the secondary carbon becomes more oxidable than the tertiary one. Because these unexpected results were obtained, the study has been extended to non fluorinated polyethers. On the basis of the results obtained, a general mechanism of the primary oxidation of polyethers is given, and the role played by the fluorine atoms on the orientation of the reactions is discussed.