Polystyrene film absorbance spectrum

Once laid, the polystyrene films were further purified by exhaustive extraction with methanol or n-heptane the progress of extraction was followed by the ultraviolet spectra of the extracts. These preirradiation extractions showed considerable variation in purity among the three polystyrenes in spite of reprecipitation measures. The degree to which solvents can remain with a 20/ film is suggested by the need of seven days of continuous methanol or n-heptane extraction to remove all of the extractable benzene from a film laid from that solvent and dried in vacuum at 65°C. for 24 hours. For film laid from methylene chloride, an optically clean n-heptane extract was obtained from the AIBN-ini-tiated sample within a few hours, but up to 48 hours were required for the benzoyl peroxide-initiated samples. The extracted 20/ polystyrene films were essentially non-absorbing above 285 m/, no absorption attributable to material other than polystyrene could be observed, and only one peak (337 m/ ) was seen in the fluorescence spectrum in methylene chloride. Once the films were purified by extraction, the products and wettability changes resulting from irradiation were the same for all polystyrene samples and were independent of the solvent from which the films were laid. 

Figure 10.2 Mid-IR spectrum of a polystyrene film. The typical representation of an infrared spectrum with a linear scale abscissa in cm (see formula 10.1) for an easier observation of the right-hand section and with percentage transmittance along the ordinate. The transmittance is sometimes replaced by the absorbance A(A = — log T). The scale, in cm , (or kaysers) is linear in energy E = hc/X) and will decrease from left to right (i.e. from high to low energy).

To demonstrate the usefulness of the ATR method for measuring infrared spectra from hard materials, the ATR spectrum in absorbance of a pellet of polystyrene is shown in Figure 13.11a, and compared with the absorbance spectrum recorded in transmission from a thin polystyrene film shown in Figure 13.11b. The film was formed from the pellet by using a hot compression molding press. Comparison of these two spectra clearly indicates that the relative intensities of bands toward higher wavenumbers in the ATR spectrum are weaker than those in the transmission spectrum, and conversely the relative... 

Figure 15.9 Absorbance spectrum of a thin polystyrene film at30°C recorded using a transmission measurement.

Fig. 4.39. The DIRLD spectra, AA (in-phase) and AA" (quadrature), and the absorbance spectrum of an atactic polystyrene film in the region between 1525 and 1425 cm. (Reproduced with permission form Ref. [39] 1988 Society for Applied Spectroscopy.)...

The absorptivities of fundamental bands in the condensed-phase spectra of most samples vary by well over an order of magnitude, but the strongest band in the spectra of typical neat liquids or solids usually has an absorbance of between about 0.5 and 2 AU if the thickness of the sample is 10 pm. This is only a rule of thumb, however. The absorptivity of strong bands in the spectra of polar analyte is almost invariably greater than that of the stronger bands in the spectra of nonpolar analytes. For example, the four strongest bands in the spectrum of a 5-pm film of poly (ethylene terephthalate) are more intense than the strongest band in the spectrum of a 20-pm film of polystyrene. 

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