Theoretical approach to the crystal structure of poly(butylene 2,5-furandicarboxylate) as revealed by density functional theory

In this work, we present a new model of the crystalline structure of the poly(butylene 2,5-furandicarboxylate) (PBF). This new structure has been derived using an ab initio density functional theory methodology and focusing on the agreement between the experimental and theoretical x-ray diffraction patterns. An extensive study has been performed to analyze the possible conformations that the polymeric strand can adopt in its crystalline form, leading to 60 initial crystalline structures. Due to thermal motion, which cannot be easily tackled with the ab initio methodology, and small inaccuracies, which are intrinsic to this calculation method, the theoretical unit cell dimensions can slightly differ from those obtained in the crystallization experiments. Thus, a structural refinement method has been employed to overcome these discrepancies and procure a crystalline structure whose x-ray diffraction pattern is consistent with the experimental one. For the proposed crystalline structure of PBF, both the powder diffraction pattern and the fiber diffraction diagram show a remarkable agreement with those available in the literature.