High-pressure photooxidation of polystyrene (original) (raw)
Related papers
Photo-oxidation of polymers—III
European Polymer Journal, 1978
Changes of molecular weight distribution resulting from vacuum photolysis and photo-oxidation of polystyrene have been determined by gel permeation chromatography. On irradiation at 253.7 nm, crosslinking is predominant in vacuo; in the presence of oxygen, crosslinking and main chain scission occur simultaneously because of light absorption by two or more different chromophores. Main chain scission is more important than crosslinking in the photolysis and photo-oxidation of polystyrene containing cumene hydroperoxide irradiated at 313 nm or containing benzophenone irradiated in the range 320-420 nm. In this last case, main chain scission and crosslinking are both strongly inhibited if the sample contains napthalene which acts as quencher of the excited triplet state of benzophenone, Only moderate inhibition is observed in the presence of 2,6-di-t-butyl-4 methylphenol. R~um6-Les changements de distribution de masse mol6culaire r6sultant de la photolyse sous vide et de la photoxydation du polystyr/me ont 6t6 d6termin6s au moyen de la chromatographie par perm6ation de gel. Lors de rirradiation fi 253.7 nm la r6ticulation est pr6pond6rante sous vide. En pr6sence d'oxyg6ne, r6ticulation et ruptures de chalne principale se produisent simultan6ment suite fi rabsorption de la lumi&e par au moins deux chromophores diff6rents. Les ruptures de chaines principales l'emportent sur la r6ticulation lors de la photolyse et de la photoxydation du polystyrene soit contenant de l'hydroperoxyde de cum6ne et irradi6 ~ 313 nm soit contenant de la benzoph6none et irradi6 dans le domaine 320-420nm. Dans ce dernier cas, les ruptures de chalne et la r6ticulation sont fortement inhib~es si l'6chantillon contient du naphtal6ne qui d6sactive le triplet excit6 de la benzoph6none; une inhibition mod6r6e est observ6e en presence de 2,6-di-t-butyl-4 m6thylph6nol.
Polystyrene photooxidation. 2. A pseudo wavelength effect
Macromolecules, 1992
The photoproducts formed in polystyrene photooxidized by exposure to long wavelengths (A L 300 nm) or short wavelength (A = 253.7 nm) absorbing in the IR range were identified and reported in the preceding paper. It was shown that, despite some differences in the distribution of oxidation photoproducts, the same products were obtained. The present paper report8 on complementary experiments carried out at a different temperature and on microspectrophotometric determination of the photoproduct profiles. The apparent differences resulting from the short-or long-wavelength irradiation are attributed to the diffusion of the low molecular weight photoproducts. A general mechanism accounting for the photooxidation of the polystyrene at short or long wavelengths is given.
Polymer Degradation and Stability, 1981
Processing of polystyrene at 160°C for different periods in the closed chamber of a Brabender Plastograph results in no appreciable oxidation. Therefore, the photooxidative stability of the polymer, as measured from retention of the ultimate tensile strength, is not affected by such treatment. On the other hand, acetophenone groups, the concentration of which increases with processing time, are produced at 160°C in the open chamber of the Plastograph as a consequence of extensive thermal oxidation. A quantitative correlation is found between the rate of change of the ultimate tensile strength of polystyrene and the extent of thermal oxidation. It is also demonstrated that a phenolic antioxidant, although it efficiently inhibits the thermal oxidation, has no specific effect on the photo-oxidation of polystyrene. A hindered amine light stabiliser, however, exhibits a pronounced photo-protective effect. A mixture of these additives combines the benefits of both.
Photo-chemical reactions in commercial poly(oxymethylene)
Polymer Degradation and Stability, 1979
Poly(oxymethylene) has been examined using infra-red, ultrariolet absorption and luminescence techniques. The first technique indicates that aldehydic carbonyl groups are present in the polymer whereas the latter two indicate the presence of ~,13unsaturated carbonyl groups. The behat'iour of these impurity carbonyl species during irradiation under sunlight-simulated conditions has also been examined. Possible mechanisms for the participation of these chromophoric units in the photooxidation of the polymer are discussed.
The Photo-Oxidation of Polymers. A Comparison with Low Molecular Weight Compounds
Elsevier eBooks, 1979
The photo-oxidation of polymers involves different steps in which their reactivity is different from that of low molecular weight conpounds. This is mainly due to the close vicinity of reactive groups in polymers and to the rigidity of the matrix. As a consequence, transfer of energy has a major role in the initiation of the photo-oxidation of most polymers on exposure to sunlight. It results in the sensitized decomposition of neighbouring hydroperoxide groups which, however, produce free radicals and thus initiate the oxidation less efficiently than model compounds in fluid solution. Scission of the polymer backbone, responsible for the alteration of the physical and mechanical properties, involves the decomposition of isolated hydroperoxide groups by two different mechanisms the relative importance of which changes with temperature.
Polymer Degradation and Stability, 1984
The changes in surface chemistry during the photo-oxidation (2 > 29Onto) of polystyrene films in air have been monitored by means of ESCA. The data reveal that the reactions involve the ring opening of the pendent phenyl groups and that the rate and extent of oxygen uptake are strongly dependent on the partial pressure of oxygen at the gas~solid interface. Comparison of cyclic and continuous irradiations indicates that photo-oxidation in the surface is influenced by the presence and extent of dark periods.
Photochemical & Photobiological Sciences, 2006
Vacuum-ultraviolet (VUV) irradiation (k exc : 172 ± 12 nm) of polystyrene films in the presence of oxygen produced not only oxidatively functionalized surfaces, but generated also morphological changes. Whereas OH-and C=O-functionalized surfaces might be used for e.g. secondary functionalization, enhanced aggregation or printing, processes leading to morphological changes open new possibilities of microstructurization. Series of experiments made under different experimental conditions brought evidence of two different reaction pathways: introduction of OH-and C=O-groups at the polystyrene pathways is mainly due to the reaction of reactive oxygen species (hydroxyl radicals, atomic oxygen, ozone) produced in the gas phase between the VUV-radiation source and the substrate. However, oxidative fragmentation leading to morphological changes, oxidation products of low molecular weight and eventually to mineralization of the organic substrate is initiated by electronic excitation of the polymer leading to CC bond homolysis and to a complex oxidation manifold after trapping of the C-centred radicals by molecular oxygen. The pathways of oxidative functionalization or fragmentation could be differentiated by FTIR-ATR analysis of irradiated polystyrene surfaces before and after washing with acetonitrile and microscopic fluorescence analysis of the surfaces secondarily functionalized with the N,N,N-tridodecyl-triaza-triangulenium (TATA) cation. Ozonization of the polystyrene leads to oxidative functionalization of the polymer surface but cannot initiate the fragmentation of the polymer backbone. Oxidative fragmentation is initiated by electronic excitation of the polymer (contact-mode AFM analysis), and evidence of the generation of intermediate C-centred radicals is given e.g. by experiments in the absence of oxygen leading to cross-linking (solubility effects, optical microscopy, friction-mode AFM) and disproportionation (fluorescence).
Photochemical reactions in commercial poly (oxy (2, 6‐dimethyl)‐1, 4‐phenylene)
Die Makromolekulare Chemie, 1979
Poly(oxymethylene) has been examined using infra-red, ultrariolet absorption and luminescence techniques. The first technique indicates that aldehydic carbonyl groups are present in the polymer whereas the latter two indicate the presence of ~,13unsaturated carbonyl groups. The behat'iour of these impurity carbonyl species during irradiation under sunlight-simulated conditions has also been examined. Possible mechanisms for the participation of these chromophoric units in the photooxidation of the polymer are discussed.