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Free volume determination of azobenzene-PMMA copolymer by a pulsed low-energy positron lifetime beam with in-situ UV illumination

Algers, John LU ; Sperr, P; Egger, W; Liszkay, L; Kogel, G; de Baerdemaeker, J and Maurer, Frans LU (2004) In Macromolecules 37(21). p.8035-8042
Abstract
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... (More)
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. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Macromolecules
volume
37
issue
21
pages
8035 - 8042
publisher
The American Chemical Society
external identifiers
  • wos:000224472500028
  • scopus:7644222885
ISSN
0024-9297
DOI
10.1021/ma0486086
language
English
LU publication?
yes
id
6d376c25-3c87-453b-b37c-a71862f3baae (old id 139495)
date added to LUP
2007-07-12 14:40:07
date last changed
2017-01-01 04:26:18
@article{6d376c25-3c87-453b-b37c-a71862f3baae,
  abstract     = {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.},
  author       = {Algers, John and Sperr, P and Egger, W and Liszkay, L and Kogel, G and de Baerdemaeker, J and Maurer, Frans},
  issn         = {0024-9297},
  language     = {eng},
  number       = {21},
  pages        = {8035--8042},
  publisher    = {The American Chemical Society},
  series       = {Macromolecules},
  title        = {Free volume determination of azobenzene-PMMA copolymer by a pulsed low-energy positron lifetime beam with in-situ UV illumination},
  url          = {http://dx.doi.org/10.1021/ma0486086},
  volume       = {37},
  year         = {2004},
}