Polymer Photochemistry最新文献

The photo-oxidation of styrene-butadiene copolymer (SBR) with light at λ>300 nm was investigated. The formation of hydroperoxide compounds accompanied by crosslinking of the copolymer was observed in the first stage of the process. The participation of a copolymer-oxygen complex as well as carbonyl and hydroperoxide compounds in initiation of SBR photo-oxidation was taken into consideration. The studies of the inhibiting effect of various additives on SBR photo-oxidation as well as energy transfer processes allowed the conclusion that the singlet oxygen is the most important reactive species in the system investigated.

Six monoazo dyes were prepared and recrystallized from the appropriate solvent. Their UV and visible spectra were measured.

The dipole moments of these dyes were obtained from measurements of their static dielectric constants and refractive indices of dilute solutions in benzene at 20°C.

The colour strength (K/S) of nylon 6 fabrics dyed with these dyes was measured.

From the results obtained, it was found that there is a relationship between the dipole moment of the dyes under investigation and their colour strength (K/S) on dyed fabrics.

The photoinitiated graft copolymerisation of 2-hydroxyethyl acrylate (2HEA) onto regenerated cellulose film has been studied. Films were presented for impregnation in both the dry film and gel film states. A novel, water-soluble photosensitiser, 4-(trimethylammoniummethyl)benzophenone chloride, has been developed and its efficiency assessed. The gel film state is shown to be highly conducive to preferential uptake of monomer and hence efficient grafting. Grafting is found to maximise at a photoinitiator concentration of approximately 2·6 × 10⁻² mol litre⁻¹. Grafting is retarded but not inhibited by p-benzoquinone and sulphonated p-benzoquinone. Evidence is given showing that impregnation of dry cellulose film with the grafting medium gives a concentration of monomer in the film which is markedly different from that in the bulk medium.

Evidence is presented which shows that aqueous solutions of 4-(trimethylammoniummethyl)benzophenone chloride, BP2, are photochemically stable within experimental conditions applied. However, in aqueous solutions of BP2 which contain compounds capable of H-atom donation, then BP2 undergoes rapid decomposition. In terms of the enhancement of photodecomposition, the observed order is poly(vinyl alcohol) > propan-2-ol > ethanol > propan-1-ol > glucose > 1,3-propanediol > 1,2-ethanediol > methanol.

By contrast, 4-(sulphomethyl)benzil sodium salt, BZ1, is rapidly photodecomposed when irradiated in aqueous solution even in the absence of additional H-atom donors.

Information is given which shows that various monomers have the ability to reduce the level of photodecomposition of aqueous solutions of BP2 which contain propan-2-ol. Thus, 2-hydroxyethyl acrylate> 2-hydroxypropyl acrylate > acrylic acid in terms of reducing the extent of photodecomposition. In addition, details are presented regarding the concentration dependence of this photodecomposition process with regard to the presence of 2-hydroxyethyl acrylate. Finally, aspects of the photodecomposition of BP2 and BZ1, present in regenerated cellulose film, are considered.

Photopolymerization of methyl methacrylate was studied at 35°C using α-picoline-sulphur dioxide, (α-Pi-SO₂) charge-transfer complex as the photoinitiator in the presence of several solvents. It was observed that the polymerization proceeded via a radical mechanism and the termination was initiator-dependent. Chain termination via degradative chain (initiator) transfer appears to be significant here.

With a view to the manufacture of printing plates, films consisting of diethylene glycol diacrylate and poly(methyl methacrylate) acting as a binding agent and containing 9-phenylacridine as the photoinitiator were irradiated by means of fluorescent lamps, each film being covered by two sheets of poly(ethylene terephthalate) to exclude atmospheric oxygen. After irradiation the cover sheets were removed and the films were extracted with chloroform in a soxhlet apparatus. Together with residual monomer and low molecular weight compounds, nearly all the poly(methyl methacrylate) could be separated. The residue represented the crosslinked and therefore insoluble polymer. Under standard reaction conditions its yield can serve as a measure for the reaction rate.

Generally, polymerization of the monomer takes place under the influence of light, even if the films do not contain any photoinitiator. However, 9-phenylacridine as a photoinitiator enhances polymerization considerably. Best results are obtained with an initiator concentration of 0·1 wt%, based on the monomer.

The initiation mechanism is different from that derived recently for the polymerization of methyl methacrylate. The photoinitiator being in an excited state after absorption of light strips off hydrogen from the monomer, probably from the CH₂CH₂ groups, thus producing free radicals. In contrast, methyl methacrylate is not suitable as a hydrogen donor; for the polymerization of methyl methacrylate an additional hydrogen donor like diethylene glycol diethyl ether has to be added.

There is no evidence that poly(methyl methacrylate) is involved in the initiation reaction.

The photophysical and photochemical properties of bisphenol-A-epichlorohydrin condensation polymers and model compounds produced from aryl glycidyl ethers are attributed to the ArO— chromophore. The absorption and emission spectra, the singlet and triplet energies and also the fluorescence lifetimes of the compounds are very similar to those of aryl alkyl ethers. In solution, major photolysis products of the model compounds are phenols and substituted phenols, arising from the photorearrangement. Major photoproducts from 1,3-diphenoxy-2-propanol on irradiation at 254 nm (in N₂) differed from those at > 280 nm (in air). At low conversion, the quantum yields of compound loss are about 0·1, but the reactions are self-inhibiting, which may be attributed to light absorption and quenching by the photolysis products. Aromatic hydrocarbons with an E_s energy higher than 420 kJ mol⁻¹ sensitize the photoreactions of the model compounds. Kinetic measurements provide support for S₁-S₁ sensitization.

The formation of spatial structures in photochemical reactions with the resulting creation of stable absorbing products is studied. A theoretical analysis is performed in the approximation of the stationary concentration of intermediate reagents. It is found that in reactions with an arbitrary order of light intensity, accumulation of absorbing products is described by the ‘degradation wave’ of a fixed form.

The wave dynamics determining the degradation velocity is characterized by the single parameter of ‘photoaction’. This parameter depends on the variation law of the incident light intensity, time of action and the chemical reaction mechanism. In the simplest case it is the radiation dose.

The profile forms and the dynamics of their establishment for reactions with different concentration levels of absorbing products are investigated. The conditions for creation of ‘limited degraded layers’ in the polymer are determined.

Experiments in poly(vinyl chloride) (PVC) revealing spatial structures and investigating the product concentration profile in them are considered. It is discovered that in air a three-layer structure forms whose parameters are dependent on the radiation regime. The experimental results are compared with the theory. The possibility of observing spatial layers in polyolefins is discussed.

Seventeen direct dyes from a commercial source were used for dyeing cotton fabrics. The lightfastness of these dyed samples was measured by two methods namely by the blue scale method and by colour difference analysis. From the results obtained, it was noted that the colour difference method is more definitive and truly measures the degree of light fading.