Influence of polyethylene glycol on the phase transition of poly(butylene adipate) thin films: Polymorphic control

Control of the polymorphic crystals formation of poly(butylene adipate) (PBA) is crucial to tailor its performance. In the present study, we investigated the effect of polyethylene glycol (PEG) with molecular weight of 400 on the polymorphic crystal of PBA thin films using x-ray diffraction (XRD), temperature-dependent infrared-reflection absorbance spectroscopy (IRRAS) and two-dimensional correlation analysis (2DCOS). XRD and IRRAS results suggest that the PBA thin film tends to grow α-form crystal with addition of PEG at room temperature. Increasing the PEG contribution to 30wt%, the PBA thin film shows α-form crystal only. Temperature-dependent IRRAS spectra indicate that pure PBA thin film exhibited α/β mixed crystal and the β-to-α transition was observed during the heating process. After the incorporation of PEG, PEG not only inhibits the growth of β crystal but also suppresses the β-to-α transition during the heating process. In addition, we unexpectedly captured three different amorphous bands of CO stretching of pure PBA from the asynchronous 2D correlation spectrum. The band at 1740cm^-1 corresponded to the amorphous phase of PBA at room temperature, whereas 1746 and 1760cm^-1 respectively arose from the amorphous phase of PBA melting from α-form crystal and β-form crystal. This study demonstrated that the crystal form of PBA can be modified by blending with PEG, providing a new method to control the crystal modification and physical properties of polymorphic PBA in their blend system.