The effect of poly(vinyl phenol) sublayer on the crystallization and melting behavior of poly(3-hydroxybutyrate) via hydrogen bonds

The cold crystallization and melting behavior of poly(3-hydroxybutyrate)(PHB) layer on amorphous Poly(vinyl phenol) (PVPh) and Si wafer substrate were studied by using Grazing incidence X-ray diffraction and infrared reflection-absorption spectroscopy. Compared to the PHB on Si wafer, the PVPh layer shows great influence on the crystallization and melting behavior of PHB layer. The depression extent of melting temperature increases with the increase of PVPh thickness when the thickness of PVPh is smaller than a critical value. Infrared reflection-absorption spectroscopy study is carried out to better understand the structure evolution of PHB and its interaction with PVPh in the heating process. By monitoring and decomposing the CO stretching bands, several points can be identified: (1) melting temperature decreases with PVPh thickening; (2) the fraction of intermolecular hydrogen bonds formed between the OH groups of PVPh and CO groups of PHB is very small below glass transition temperature of PVPh and it increases significantly above 100 °C. Moreover the fraction increases with PVPh thickness. The effect of PVPh thickness on the formation of hydrogen bonds is attributed to the roughness, molecular mobility and/or molecular orientation of PVPh.