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Dielectric relaxation spectroscopy of amorphous and liquid‐crystalline side‐chain polycarbonates
Author(s) -
Wübbenhorst Michael,
Van Koten Ernout M.,
Jansen John C.,
Mijs Wim,
van Turnhout Jan
Publication year - 1997
Publication title -
macromolecular rapid communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.348
H-Index - 154
eISSN - 1521-3927
pISSN - 1022-1336
DOI - 10.1002/marc.1997.030180211
Subject(s) - mesogen , side chain , glass transition , relaxation (psychology) , amorphous solid , dielectric , materials science , pendant group , ether , liquid crystal , polymer chemistry , polycarbonate , crystallography , polymer , chemistry , organic chemistry , liquid crystalline , composite material , social psychology , optoelectronics , psychology
The molecular dynamics of amorphous and liquid‐crystalline (LC) side‐chain polycarbonates was studied by dielectric spectroscopy at frequencies from 10 −2 to 10 6 Hz and at temperatures from −160 to 180°C. ‘Model’ compounds containing no mesogenic side‐groups showed two relaxations, which originate from the carbonate group (α, β m ‐relaxation). By contrast, in LC‐polycarbonates bearing a mesogenic nitrostilbene side group around and above the glass transition temperature T g up to three relaxation modes were distinguished (α‐, λ 1 ‐, λ 2 ‐process); below T g four secondary relaxations (γ‐, β m ‐, β s ‐, β sc ‐relaxation) were observed. The γ‐relaxation was found only in compounds possessing an aliphatic spacer linked to the backbone by an ether bond. Apart from β m ‐, two additional β‐processes were identified as relaxations associated with the mesogenic unit in the glassy (β s ) or in the crystalline state (β sc ).