Factors Affecting Determination of Free Volume in Membrane Materials via the Spin Probe Methodтезисы доклада

Дата последнего поиска статьи во внешних источниках: 17 октября 2017 г.

Работа с тезисами доклада


[1] Factors affecting determination of free volume in membrane materials via the spin probe method / Y. Yampolskii, I. Barashkova, M. Bermeshev, N. Belov // Book of Abstracts International conference on membranes ICOM2014. — Suzhou, 2014. — P. 1470. The spin probe technique is known among the methods for estimation the size of free volume elements in polymers [1]. It is based on the measurement, by the ESR method, of the frequency of rotation ν (s -1 ) of stable free radicals (most often nitroxyl radical TEMPO) dissolved in polymers. A rapid rotation of the spin probe can indicate that the size of free volume element in the polymer is larger than the size of the probe (170 A 3 in the case of TEMPO). It is also important to assess a possible influence of other factors on the rate of rotation of the probe in polymer materials. In this work we report the results of the study of the rotation frequency of TEMPO introduced into 3 groups of glassy polymers: (1) ring-opening metathesis polynorbornenes with the side groups containing flexible Si-O-Si bonds; (2) polymers of inner microporosity PIM-polyimides; (3) perfluorinated polymers such as poly(hexafluoropropylene), Nafion, Hyflon etc.. It was shown that different factors affect the frequency of rotation of TEMPO in these polymers. In polynorbornenes the frequency ν correlate with gas permeability but not the fractional free volume FFV. It is much higher than in non-substituted polynorbornene. A conclusion can be made that local movements of side groups in these polymers affect the mobility of the spin probe. So these polymers having the glass transition temperature in the range 100-240 o C behave like a rubber. In PIM-PIs the reasons for the mobility of TEMPO are caused by relatively large free volume elements in these polymers, so TEMPO probes can be accommodated within them. Interesting results were also obtained for perfluorinated polymers. References 1. Yu.P.Yampolskii, Methods for investigation of free volume in polymers, Russ. Chem. Rev., 76, 59 (2007) Acknowledgement. This work was supported by OkhNM-3 Program of Russian Academy of Sciences.

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