Polystyrene solution decay rate

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. 

The thermal decay process of the radicals is a bimolecular reaction. The decay rate increases with increasing temperature. At 100° C, a half-life of 12 minutes has been observed for methyl methacrylate popcorn radicals. A fast decay rate takes place when the dry popcorn is swollen in a liquid such as benzene. That means that during the proliferous growth process, when the polymer is swollen by the monomer, a decay process also occurs, and a stationary radical concentration in the growing polymer popcorn results. A liquid that does not swell the polymer (for example, methanol for polystyrene) does not influence the decay rate. A much higher rate of radical decay is obtained with a benzene solution of diphenylpicrylhydrazil. The reaction rate between the polymer radical and inhibitor radical may be measured. 

Delphin and Horwitz investigated sodium isotopic separations in chromatographic experiments using dicyclohexano] 18]crown-6 and [18]crown-6 (see Fig. 11). A steel column was applied which was 50 cm in height and 0.3 cm in diameter and filled with the strongly acidic polystyrene resin Aminex A 7. A mixture of Na and Na which had a nearly equal decay rate for both isotopes was fixed at the top of the column and was then eluted by a solution of methanol/water (80 %/20 %,... 

Thus, any deviation from first-order kinetics will indicate that the azobenzene residues in the system under study isomerize at different rates. Such a dispersion of the rate constant for hindered rotation was postulated by other investigators. Cochran et al reached this conclusion on the basis of the molecular weight dependence of the relaxation times observed with polystyrene by sound absorption studies. Valeur and MonnerieS subjected a solution of polystyrene with anthracene residues incorporated into the chain backbone to a nanosecond light flash and found that the time-dependence of the anthracene fluorescence deviated from a simple exponential decay this was ascribed to differences in the local conformational mobility of the chain. 

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