Absorption spectra polystyrene

The absorption spectrum observed in the pulse radiolysis of solid films of polystyrene is shown in Figure 5. The absorption spectrum around 540 nm is also very similar to the absorption spectrum of polystyrene excimer observed in irradiated polystyrene solutions in cyclohexane as reported previously (2,3). The absorption with the maximum at 410 nm was reported previously and was assigned to anionic species (13,14). The longer life absorptions, attributed to triplet excited polystyrene repeat units and nonidentifiable free radicals, were observed in a wave length region < 400 nm. The absorption spectrum of CMS films obtained in pulse radiolysis showed a peak around 320 nm and a very broad absorption around 500 nm as shown in Figure 6. 

The absorption band around 520 nm is very similar to that of polystyrene excimer (2,3,5). The decay follows first order kinetics with a lifetime of 20 ns. The decay rate agrees with that of the excimer fluorescence and excimer absorption. The longer life absorptions, attributed to the triplet states and free radicals (2,5), were observed at wave lengths <400 nm, although the anionic species of polystyrene with the absorption maximum at 410 nm as seen in solid films (cf. Figure 5) was not observed. Figure 9 shows the absorption spectrum observed in the pulse radiolysis of CMS solution in cyclohexane. 

Figure 8. Transient absorption spectrum obtained by pulse radiolysis of 200 mM polystyrene solution in cyclohexane.

The absorptions at both 500 nm and 320 nm follow first order kinetics with a lifetime of 420 ns. This absorption species is neither the excimer of polystyrene nor free cationic species of polystyrene. Although the excimer of polystyrene has an absorption band around 500 nm, the lifetime is only 20 ns. Further the free cationic species of polystyrene should live for a longer time in this solution, and the absorption band should exist in a longer wavelength region (6). These considerations of lifetime and absorption spectrum lead us to conclude that the absorption spectrum shown in Figure 12 is due to the charge transfer-radical complex between polystyrene and Cl radical (2,4,17). A very similar... 

The transient absorption spectrum obtained in the pulse radiolysis of polystyrene solution in CC1 is shown in Figure 13. The spectrum is very similar to the charge transfer radical complex (PS4+C14-) species. The lifetime is about 200 ns. Consideration of the absorption spectrum and the lifetime suggest that this species is (PS4+C14-)-. The processes leading to formation of this species in liquid CC14 can be written as follows (4,7). 

Reaction Scheme of CMS Resists. The transient absorption spectrum shown in Figure 6 and observed for irradiated CMS films is mainly composed of two components as based on pulse radiolysis data of solid films of CMS and polystyrene, and CMS and polystyrene solutions in cyclohexane, chloroform, and carbon tetrachloride. An absorption with a maxima at 320 nm and 500 nm as due to the charge transfer radical-complex of the phenyl ring of CMS and chlorine atom (see Figure 14) and an absorption with maxima at 312 and 324 nm is due to benzyl type radicals (see Figure 11). 

Fig. 11. Transient absorption spectrum observed at 170 ns after a pulse in 200 base-mmol dm " 3 polystyrene in CHClj [58]...

To relate the wettability changes more firmly to the photooxidation processes and products, a detailed study was carried out with polystyrene. This polymer was selected because the formation of oxidation products in the hydrocarbon surface gave rise to large changes in wettability and because these products would be readily accessible to optical methods of analysis. The ultraviolet absorption spectrum of polystyrene shows a sharp cut-off, and the extinction coefficients for the radiation absorbed are sufficiently high that almost all of the photochemical reaction should be confined to the surface layers. 

Fig. 1 shows the transient absorption spectra observed during photolysis of cyclohexane solutions of CMS. The absorption spectrum with the peak at 520 nm (spectrum a) is identical to that of the excimer of polystyrene (spectrum C) (22) and has a similar lifetime of 20 ns. The quenching rate of the absorption at 520 nm by O2 is comparable to what one would expect for the CMS excimer. 

The very broad absorption between 300 and 400 nm is comparable to the absorption spectrum of the triplet state of polystyrene (22). The lifetime of this intermediate is essentially independent of the chloromethylation ratio and is comparable to the lifetime of the triplet state of polystyrene (110 ns). 

A rapid initial drop in molecular weight followed by a slower decrease is observed when polyvinylpyridine is heated at 250°C [85]. This behaviour is qualitatively similar to that of polystyrene. Scission of weak links may be involved in the fast decay of molecular weight, but random scission may also explain the shape of the curve. As in the case of polystyrene, the mechanistic problem is very complex and many more experiments are needed to solve it. Chelation of 2- and 4-polyvinylpyridine makes those polymers less heat-resistant chain scissions already occur at 100°C while the uncomplexed polymer suffers no damage at this temperature. On heating, a change in the absorption spectrum of 2-polyvinylpyridine copper chelate dissolved in 1M HC1 is observed a new peak is formed at... 

The fascinating properties exhibited by nanoparticles, such as blue shift of the absorption spectrum, size-dependent luminescence, etc., are various manifestations of the so-called quantum confinement effect. These unique properties make ZnO a promising candidate for applications in optical and optoelectronic devices [35-38]. Polymer-based nanocomposites are the subject of considerable research due to the possibility of combining the advantages of both polymers and nanoparticles. There are several applications of polymeric nanocomposites based on their optical, electrical and mechanical properties. Further, nanocrystals dispersed in suitable solid hosts can be stabilized for long periods of time. Polystyrene (PS)— an amorphous, optically clear thermoplastic material, which is flexible in thin-film form—is often chosen as a host matrix because of its ideal properties for investigating optical properties. It is one of the most extensively used plastic materials, e.g., in disposable cutlery, plastic models, CD and DVD cases, and smoke-detector housings. 

Both polystyrene samples contained an ester and a mineral oil type of lubricant together with a phenolic antioxidant. The lubricants have little absorption in the 280-300 nm region and do not interfere in either method of analysis at the 5-10% concentrations at which they are used in polystyrene formulations. The absorption spectrum of the phenolic antioxidant, however, shows a sharply decreasing non-linear absorbance in the 280-300 nm region and contributes significantly to the background absorption of the test solution in the direct UV spectroscopic method. This invalidates the baseline correction procedure and leads to erroneous styrene monomer values. In the distillation procedure, however, the test solution used for spectroscopy does not contain the phenolic antioxidant and there is no interference in the determination of styrene monomer. 

FIGURE 16-1 IR absorption spectrum of a thin polystyrene film. Note the scale change on the c-axis at 2000 cm. ... 

D binds stoichiometrically to the SO3 groups of polystyrene sulfonic acid (PSS). The binding process was followed by titrating D with PSS in aqueous solution a change on the absorption spectrum was observed and was attributed to the formation of intermolecular associated species among dye molecules crowded along the polyanion chain. 

Figure 17.3 shows the UV absorption spectrum of polystyrene. In the spectrum, absorption peaks for polystyrene are found at 260, 215, 194, and 80 nm. The first three peaks are the result of the transition of n electrons, whereas the 80-nm peak involves ct electrons. 

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