Spectroscopic characterization of the .alpha. .dblharw. .beta. crystalline phase transition in poly(butylene terephthalate) and its copolymers with poly(tetramethylene oxide)

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

“…Poly(butylene terephthalate) (PBT), the second member of this family in order of technological importance after poly(ethylene terephthalate) (PET), shows a reversible transition between different crystal structures upon mechanical deformation, which corresponds to a variation in the conformation of the chain. − Many authors have investigated this polymorphic transition by means of different characterization techniques, ranging from X-ray diffraction (XRD) − ,,, to electron microscopy, vibrational spectroscopy, − ,− nuclear magnetic resonance, and molecular mechanics simulations . Despite this large interest, some features are still debated, such as for example the structure of the polymer in the stress-induced β phase: while most of the authors agree in proposing an all-trans structure, other ones have proposed a different conformation for the PBT chains in the crystal.…”

Finite strain response, microstructural evolution and β→α phase transformation of crystalline isotactic polypropylene

“…Stress-induced a4b phase transformation of poly(butylene terephthalate) (PBT) was studied by Dobrovolnay-Marand et al and found to be accomplished via the change of molecular conformation [30]. In a form, the plane of benzene rings is inclined about 198 to the c axis of the unit cell, whereas it is nearly parallel to the c axis in b form.…”

Dielectric relaxation spectroscopy of poly(ethylene terephthalate)

“…The latter is considered more likely for PET where the polarization processes may occur between individual crystallites within less‐conductive crystalline domains 51. 52…”