Polymorphism of Poly(butylene terephthalate) Investigated by Means of Periodic Density Functional Theory Calculations

The conformation and solid state structure of the two α and β polymorphs of poly(butylene terephthalate) are here studied by means of state-of-the-art first principles calculations, carried out both for the crystals and the infinite one-dimensional chain models. Focusing in details on the debated β form, induced by mechanical deformation, we verified the setting on of an all-trans conformation, as also supported by the simulation of the infrared spectra of the different polymorphs compared to the available experimental spectra. The transition from the α to the β form is also simulated by applying increasing strains to the infinite polymer chain: a peculiar evolution of the intramolecular structure is indeed predicted, showing a transition from the GTG′ conformation found for the α form to the TTT conformation of the strained β form.