Poly during irradiation

Fig. 16. Change of optical density (JD) of aqueous solutions of poly (potassium propynoate) for different wavelengths in the process of oxidation during irradiation with white light...

Fig. 34. Absorbance changes of poly C during irradiation with UV, followed by heating the solution at the temperatures indicated. The poly C was irradiated at 0°C, then diluted with 0.15M NaCl (0.3 ml of poly C solutions containing 90 p,g diluted to 3.0 ml), and the absorbance change followed upon heating (Ono, Wilson, and Grossman82 ).

Data for an 88% poly (vinyl chloride )-12% poly (vinyl acetate) copolymer are shown at the top of Figure 3. In this case, the creep rate during irradiation is quite high the normal creep before the start of... 

In the cases of poly (methyl methacrylate) (PMMA) and poly (vinyl chloride-vinyl acetate) (PVC/PV Ac), these polymers generate much more gas during irradiation than polystyrene. Thus, even if the gases accumulated in microvoids, where their enhancement of creep rate might be lessened, the local gas concentration between the polymer chains should still be much higher than in the case of polystyrene. One would thus expect to see an effect of film thickness on creep rate for these polymers. 

Several new amino acid residues were detected in irradiated poly-a, r glutamic acid, poly-D,h-alanine, and poly-irproline. The pH of the solution during irradiation affects the physical and chemical changes induced in the polyamino adds. 

Silyl radicals have also been observed during /-irradiation of solid polysilanes. Tagawa and coworkers examined the EPR spectrum observed upon irradiation of solid poly-(dimethylsilane) and concluded that the spectrum corresponded to silyl radicals generated by homolysis of the silicon skeleton in the polysilane (equation 5)18. Indeed, the EPR spectrum of the poly(dimethylsilane) radical (13), with hyperfine splitting constants H) and a(y-1 H) of 0.813 and 0.046 mT respectively, corresponded remarkably well to that published for the dimethyl(trimethylsilyl)silyl radical [a( -1H) = 0.821 mT a(/-1H) = 0.047 mT]1. Radical (13) appears to be very stable in solid poly(dimethyl-silane), since the EPR signal was strong and clearly observable at room temperature. 

The fluorescence and phosphorescence excitation and emission spectra of commercial polypropylene and poly(4-methylpent-l-ene) are examined using a fully compensated spectrofluorimeter. The excitation spectra of the polymers are compared with the absorption spectra of model chromo-phores of those believed to be present in the polymers. The fluorescence emission is associated primarily with the presence of enone and the phosphorescence is associated with dienone impurity chromophoric units. Bromination of cold hexane extracts of the polymers reduces significantly the intensity of the fluorescence confirming the presence of ethylenic unsaturation. The behavior of the luminescent enone and dienone groups during irradiation under sunlight-simulated conditions is examined also. Possible mechanisms for the participation of these chromophoric units in the photooxidation of the polymers are discussed. 

In this paper we report on the identification of the luminescent impurity carbonyl species in two of the most light-sensitive polyolefins, polypropylene and poly(4-methylpent-l-ene) and examine the behavior of these groups during irradiation under sunlight-simulated conditions. 

Figure 7. Prompt-emission changes during irradiation of poly(styrene-a t-methyl methacrylate) films O, vacuum , air superscripts and subscripts refer to emission and excitation wavelengths (nm), respectively...

The growing concern over the toxicity of residual ethylene oxide after sterilization of polymers for use in the field of medicine has led to the rapid growth of the field of radiation sterilization. The medical industry consumes a massive volume of polymeric material in both equipment and implants. As a consequence there is much interest in the effects of radiation on the physical properties and stability of irradiated polymers. The standard dose for radiation sterilization is 25 kGy, which is sufficient to alter the properties of many polymers, being for example close to or above the gel dose of many elastomers. There is also interest in the reaction of oxygen with long-lived radical species formed during irradiation. A common polymer used in medical equipment, poly(propylcne) is susceptible to oxidative degradation, and must be blended with appropriate stabilizers before radiation sterilization. 

A positive effect of fillers may be observed during irradiation crosslinking. It was found that the yield of radicals in polyethylene was increased 50% when a small amount (0.05 %) of aerosil was added [21]. It has been assumed that a higher production of radicals takes place at the interphase aerosil-polyethylene, where macromolecules can be in the nonequilibrium state cf uncompensated strains. With a higher content of a filler, a transfer of energy from the filler to the polymer j se may occur and thus contribute to a higher yidd of free radicals. Combination of irradiation with reactive admixtures may, moreover, affect a localization of crosslinks along the poly-mo chain. 

It was found [122] that the current conducted by this polymer during irradiation is 40-50 times higher than it is in the dark. On the other hand, the electron mobility of the di-f-butylcarbazolepo-lyacetylene (shown above) is lower than in poly(vinyl carbazole). This was attributed to the bulkiness of the butyl groups [254]. 

Chemical changes occur during irradiation if the incident light rays are absorbed by the substance. The spectra of polycaproamide, poly-hexamethyleneadipamide, and polyhexamethylenesebacamide, cited in Fig. 130, show that waves shorter than 350 mju are most sensitive for polyamides, since there is little absorption above 350 mju [67, 68]. 

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