Polymer Photochemistry最新文献

A study of fluorescence quenching of polystyrene and statistic styrene copolymers with methyl methacrylate, ethyl acrylate and acrylonitrile by carbon tetrachloride in 1,2-dichloroethane has been carried out. The results of the study have been interpreted on the basis of the modified Stern-Volmer relation, which takes into account the fact that isolated styrenes do not participate in the process of energy migration. The coefficients of energy migration were determined for the systems studied. It was shown that the intramolecular excimers restrict the process of energy migration in polystyrene and its copolymers. The results obtained are discussed.

Assuming only the conditions for the Lambert Law, and from considerations of inner filter effects, we derive an expression which yields the net fraction of light absorbed by the bottom layer of a film having any optical density and divided into any number of hypothetical layers. We show that there is an optimum total optical density at which absorption by the bottom layer is maximized. The optimum optical density is a function of the thickness of the bottom layer probed. For an infinitesimally thin bottom layer, the optimum total optical density is 0·4343.

Triplet acetone generated from the thermal decomposition of tetramethyl-1,2-dioxethane was shown to be incapable of initiating the free radical polymerization of methyl methacrylate and styrene. Triplet acetone is rapidly quenched by energy transfer to the monomer, but the excited state of the monomer so produced does not initiate polymerization. Acetone does not initiate polymerization when irradiated into its $\text{n}\text{−π}{}^{\mathrm{\ast }}$ singlet state with UV irradiation in the absence of a co-sensitizer, but is effective when photolysed in the presence of triethylamine which quenches the acetone, possibly by resulting in the efficient formation of ketyl radicals. In contrast, methyl tert-butyl ketone is an effective initiator because of the more rapid rate of formation of radicals by α-cleavage when one of the substituents gives rise to a tertiary alkyl radical.

Commercial isotactic polypropylene films containing various additives, namely a hindered phenol (BHT), an UV absorber (Tinuvin 326), a hindered piperidine (Sanol LS 770), and mixture of BHT and Sanol were photo-irradiated with or without a glass filter at ambient temperature, and chemiluminescence spectra of the films were measured. The chemiluminescence intensity of the photo-irradiated PP films increased with irradiation time, and the shape and the intensity were noticeably affected by the nature of the additives. In the photo-irradiated PP films containing BHT, an additional new peak was observed at ca 80–100°C, and the intensity of the new peak was remarkably enhanced by the combined use of BHT and Sanol. From the results obtained the origins of the chemiluminescence sources were discussed.

The quantum yields of accumulation of oxygen-containing groups, formation of free radicals and consumption of sensitisers were determined during irradiation of rigid polyvinyl chloride (PVC) films in air at room temperature. Sensitised oxidation of the polymer was shown to be characterised by the following features: (1) linear dependence of oxidation rate on light intensity; (2) insignificant hydroperoxide yield in comparison with carbonyl compound yield; (3) linear dependence of carbonyl group accumulation from the very start of the process; (4) short length (2–4) links of the polymer oxidation chain; (5) decay of peroxide radicals in air in accord with first-order reaction; (6) low (⋍0·5) yield of alkyl radicals from thermal transformation of peroxide radicals in vacuum; and (7) valency migration to considerable distances. A kinetic scheme for the process of sensitised oxidation has been suggested. The constants of the individual stages of the process have been estimated on the basis of experimental data.