Polymer Photochemistry最新文献

The temperature-dependent photodegradation of styrene, methyl methacrylate and butyl acrylate copolymers with phenyl vinyl ketone in the solid state and in solution on irradiation with monochromatic light at 313 nm was investigated. The quantum yields of main chain scission, Φ_cs, were calculated. It was found that the Φ_cs values in solution are higher than those in a film at ambient temperature. It is shown that these values do not equalize at temperatures above the glass transition temperature, T_g, of the copolymers.

This is confirmed for the model system butyl acrylate-phenyl vinyl ketone copolymer, studied for the first time. We assume that the experimental temperature has a greater influence on the photooxidation processes of the copolymers examined than thier physical state.

Polymerization of methyl methacrylate in visible light was studied at 35°C using quinaldine-chlorine (QU-Cl₂) charge-transfer complex as the photoinitiator in the presence of several solvents. Analysis of kinetic and other data indicate that the polymerization proceeds via a radical mechanism and the termination is initiator dependent. Chain termination via degradative chain (initiator) transfer appears to be significant here.

The study of the excited state behaviour of 2,4-diarylpentanes and 1,1′-diaryl diethyl ethers illustrates the importance of configurational and conformational aspects in the intramolecular excimer formation of di- and poly-chromophoric systems. This model approach is a first step in the understanding of complex polymer photophysics.

Niobium(V) and tantalum(V) react with Alizarin Red S(AlRS) and quinizarin-3-sulphonic acid (QuS) to give the corresponding solid metal chelates. Their infrared and electronic absorption spectra were studied in the solid state. The temperature dependence of the DC electrical conductivity, activation energy for conduction and energy gap were evaluated and discussed in detail and in relation to their molecular structures and optical properties. The effects of a γ-absorbed dose (5×10⁷ rad) on the IR and electronic absorption spectra and DC electrical conductivity were demonstrated and discussed. For 1:2 complexes, superconductivity or metallic conductivity was induced by the action of ionizing radiation. A suggested mechanism was put forward for the γ-absorbed dose induced superconductivity in the 1:2 complexes of AlRS and QuS polycrystals. The possibility of their application as absorbers and/or detectors for energetic ionizing radiation was established.

Poly(vinyl chloride) (PVC) films containing FeCl₃ showed absorption spectra in the 300–400 nm region which were characteristic of FeCl⁻₄. On irradiation of the films in air the absorptions were reduced in intensity but were restored in a subsequent dark reaction to levels which were higher than those before irradiation. The relation between these systems and doped polyacetylene is discussed.

The photoinduced graft copolymerization of methyl methacrylate onto wool fibre was investigated using an isoquinoline-sulphur dioxide charge-transfer complex as the initiator. The percentage of graft yield increases with increasing concentration of the monomer and the initiator. The reaction was carried out at three different concentrations and the overall activation energy was computed. The kinetic data and other evidence indicate that the overall polymerization takes place by a radical mechanism. A suitable kinetic scheme has been suggested.

Investigations have been made on erythrosine sensitized photolysis of 4-diethylaminobenzene diazonium salt 1 and 2-diazo-1-oxo-1,2-dihydronaphthalene 2 in polymeric binders of different glass transition temperatures (T_g 30–185°C). In the case of 1 the efficiency of photolysis as well as the quenching of direct and delayed fluorescence increase with decreasing T_g; in the case of 2, however, they increase with increasing T_g. The addition of plasticizers causes analogous effects. It is assumed that the sensitization of 1 occurs preferentially from the S₁-state, whilst in case of 2 it is from the T₁-state of erythrosine. Probability calculations reveal that the effective concentrations of the reactants within the critical radius of electron transfer are low, accounting for the low efficiency of the sensitized photolysis.

Phlobaphene from Pinus radiata D. Don bark upon photolysis in the presence of oxygen causes a rapid bleaching. The final product from the photooxidation was isolated and analysed showing it to be an oligomer of low molecular weight with 3·5±0·5 carboxylic acid units per catechin unit. The same product was obtained from photolysis of catechin under the same conditions. Phlobaphene showed excellent sensitizer properties using guanosine as a singlet oxygen detector.

Free radicals produced during interaction of visible, ultraviolet and ionizing radiations with cellulose have been identified by reference to the available experimental ESR evidence and recent ESR-ENDOR spectroscopy. The subsequent chemical transformations of these radicals were deduced by reference to the products derived by radiation chemical studies of carbohydrate systems.

Photochemical conversion of paramagnetic centres formed under γ-irradiation of polyacrylic acid (PAA) at 77 K has been studied. Middle macroradicals of PAA are involved in the photodissociation reaction to form hydroxyl radicals. They are also found to be capable of recombining. A scheme for the photoradical processes in PAA at 77 K is proposed.