Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Poly(4,4'-oxydiphenylene-oxydiphthalimide) (POO) was thermally treated at 773 K for 1, 15 and 60 min under argon atmosphere resulting in free-standing films with intermingled characteristics between polymer and carbon-rich derivatives. Degradative thermal analysis performed by pyrolysis-gas chromatography/mass spectroscopy (Py-GC/MS) revealed CO2 among the major products of thermal decomposition which according to electron paramagnetic resonance (EPR) passed through a radical process. X-ray diffraction (XRD) revealed thermal treated samples with semicrystalline organization that was attributed to the development of lamellae structure. Moreover, Atomic force microscopy (AFM) showed an increase in the roughness of the samples that acquired pronounced roughcast-like surface. Hence, there was an enhancement of mechanical strength and dielectric permittivity. From the data collected a mechanism of thermal decomposition was proposed. (C) 2016 Elsevier Ltd. All rights reserved.129 399407CNPq [142910/2010-4]FAPESP [CEPID 2013/07793-6]U.S. Department of Energy by Lawrence Livermore National Laboratory [DE-AC52-07NA27344]Brazilian Synchrotron Light Source (LNLS) [GAR-14024]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)