Molecular relaxations in polyfluorene based cast films

This article reports a study of the thermal relaxation in cast films of two polyfluorene based polymers, poly{9,9-dioctylfluorenyl-2,7-diyl} (BE329) and poly{(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene]} (GE108). The relaxation processes were identified by Dynamical Mechanical Thermal Analysis (DMTA), which revealed three processes in both samples: β process at lower temperatures and two relaxations at higher temperatures (named as αA and αB). The relaxations mechanics were elucidated by Solid-State Nuclear Magnetic Resonance (NMR) methods. The results revealed that the β relaxation is related to molecular motions in the side-groups, while the second and third relaxations can be attributed to local rotations in the backbone and to a glass transition. The molecular relaxations were also identified by the temperature dependence of the fluorescence spectra, which were also associated with their molecular nature.