Directional Epitaxy Intensifying Intermolecular =C–H···O=C Hydrogen Bonding to Expedite Bulk Crystallization of Biobased Poly(butylene 2,5-furandicarboxylate)

Intermolecular =C–H···O=C hydrogen bonding plays a vital role in stabilizing the high-energy crystal conformation of poly(butylene 2,5-furandicarboxylate) (PBF), which endows a strong structural element to control its crystallization. Here, by evaluating interfacial affinity and lattice matching, a layered nucleating agent (NA) is employed for triggering the directional epitaxy via intensifying =C–H···O=C interaction to promote bulk crystallization of PBF. The expedited isothermal crystallization kinetics are analyzed by the Avrami model and proven by a sharp decline of the crystallization halt-time. The crystals induced by the layered NA not only show the enlarged crystallite size along the direction perpendicular to the (010) plane but display the preferred (010) diffraction at the beginning coupled with the compact crystallographic b-axis. Moreover, two kinds of periodic structures are produced, and the first evolved one reflects the increased long period and crystalline layer thickness. Conclusively, the intensified =C–H···O=C bonding in the NA-induced crystals is well convinced by the greater red-shifts of stretching vibrations of both =C–H and C=O after crystallization in accordance with its shrunken b-axis. Finally, a precisely epitaxial relationship between the crystal lattices of PBF and NA is proposed as the primary nucleation mechanism. This work provides an excellent example of designing effective NA inducing the directional epitaxy via intensifying the unique =C–H···O=C interaction to enhance bulk crystallization of furan-aromatic polyesters with solid multiscale structure evidence to uncover the intrinsic molecular mechanism.