Free volume determination of azobenzene-PMMA copolymer by a pulsed low-energy positron lifetime beam with in-situ UV illumination
Författare
Summary, in English
The free volume properties of a poly(methyl methacrylate)-azobenzene copolymer were for the first time directly probed by use of a low-energy positron lifetime beam with in-situ excitation capabilities, showing that the free volume cavity size was not appreciably influenced by photoisomerization and thermal isomerization in the temperature range 34-180 degreesC. lsomerization is therefore suggested to occur without any molecular rearrangement of the glassy polymer matrix, which would also account for the lack of any shift to shorter wavelengths for the photoisomerization occurring in a glassy polymer in comparison to a chloroform solution. A decrease in the thermal isomerization rate at room temperature caused by the glassy polymer is explained in terms of a model in which only a fraction of the azobenzene is free to isomerize. The cis-azobenzene was found to be an efficient inhibitor of positronium formation, which enabled measurements of thermal isomerization rates and changes in the steady-state concentration of cis-azobenzene for an illuminated sample as a function of temperature.
Avdelning/ar
Publiceringsår
2004
Språk
Engelska
Sidor
8035-8042
Publikation/Tidskrift/Serie
Macromolecules
Volym
37
Issue
21
Dokumenttyp
Artikel i tidskrift
Förlag
The American Chemical Society (ACS)
Ämne
- Chemical Sciences
Status
Published
ISBN/ISSN/Övrigt
- ISSN: 0024-9297