Dielectric relaxation spectroscopy of amorphous and liquid‐crystalline side‐chain polycarbonates

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 ).