Among "green" alternatives for oil-based commodity plastics like Polyethylene, Polyamides, and Poly(-Ethylene Terephthalate), a new class of polyesters synthesized from furandicarboxylic acids (FDCAs) currently is in the spotlight of both the academic and industrial communities. Of particular interest is Poly(Ethylene-2,5-Furanoate) (PEF), which can be synthesized from monomers derived from sugars and exhibits physical properties that imply large substitution potential for PET in bottle, fiber and packaging applications. In this study the structure-thermal properties relationship of PEF have been investigated in order to explain the complex behavior exhibited by PEF during isothermal crystallization. Secondary crystallization and melt-recrystallization processes have been identified in order to explain the observed behavior. The existence of a critical crystallization temperature around 170 degrees C marking a transition in terms of crystalline phase induced is also pointed out. Moreover, data such as the molecular weight between entanglements (M-c) and standard melting enthalpy (Delta H-m degrees) have been determined. In addition the crystalline morphology was characterized by means of SAXS and WAXS. The influence of the crystallization conditions on this morphology is given. As a main result it has been found that depending on the crystallization temperature (T-c), a disordered or an ordered crystalline phase (called alpha' and alpha respectively) are formed at low (T-c <= 170 degrees C) and high (T-c <= 170 degrees C) temperatures, respectively. Finally, evidence for the formation of a rigid amorphous phase during crystallization is presented, indicating that a three-phase model has to be considered in order to provide an appropriate description of the morphology in semi-crystalline PEF. (C) 2015 Elsevier Ltd. All rights reserved.