Infrared spectroscopy , attenuated total solvent absorption

Attenuated total reflectance infrared spectroscopy was employed to determine the possible chemical modification of the PVC specimen exposed to t-butyl alcohol and methyl t-butyl ether. Infrared spectroscopy has been used to study solvent absorption (17), oxidation (18) and other degradation reactions of polymers (19). In the studies of the hostile effects of methyl t-butyl ether and acetone, the solvent was concentrated and examined using conventional infrared techniques. 

To determine the effects of exposure to hostile enviroments, such as strong oxidizing acids, coupons of the polymers were immersed for seven days at ambient temperatures in concentrated nitric acid and 10% nitric acid. These coupons were also exposed to glacial acetic acid and hydrochloric acid according to ASTM procedure D-543-67. Visual observations were made upon removing the coupons from the acid enviroment (Table II) and the coupons were examined by means of attenuated total reflectance infrared spectroscopy which has been used to study solvent absorption (25), oxidation (26) and other degradation reactions of polymers (27). 

Platinum and palladium are effective catalysts for alcohol oxidation when used alone however, significant stability and selectivity improvements have been observed on incorporation of a second (usually less active) metal promoter such as Bi, Pb, and Sn [63-65]. These observations are common to aerobic selox of allyhc and benzylic alcohols, as well as polyols such as propylene glycol [64] and glycerol [66]. In the case of Bi, in situ X-ray absorption spectroscopy (XAS) and attenuated total reflection infrared spectroscopy (ATR-IR) indicate that the promoter protects Pt against deactivation by overoxidation and prevents site blocking by, for example, aromatic solvents [67]. 

An example of direct examination is Ae examination of the polymer film by infrared or ultra-violet spectroscopy or of Aicker sections of polymer by attenuated total reflectance (ATR) infrared spectroscopy. Such techniques have severe limitations in that, because the additive is in effect heavily diluted with polymer, detection limits are usually well above the low concentration of additive present and Ais method is only applicable if the additive has distinct sharp absorption bands in regions where the polymer itself shows little or no absorption. In-situ spectroscopic techniques are not likely to be of value, then, in the analysis of samples of unknown composition. If known amounts of additive can be incorporated into additive-free polymer, however, these techniques are likely to be extremely useful in Ae study of solvent extraction procedures, and the study of additive ageing processes (ie. the effects of heat, light, sterilization, radiation, etc.), since the rate of disappearance of or decay can be measured directly by the decrease in absorbance of Ae sample at a suitable wave-lengA. 

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