Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)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: 0 process at lower temperatures and two relaxations at higher temperatures (named as alpha(A) and alpha(B)). The relaxations mechanics were elucidated by Solid-State Nuclear Magnetic Resonance (NMR) methods. The results revealed that the beta 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. (C) 2009 Elsevier B.V. All rights reserved.15921-22SI22892292Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)MCT/PADCT/IMMPFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)