Melt Crystallization and Crystal Transition of Poly(butylene adipate) Revealed by Infrared Spectroscopy

The structure evolution of poly(butylene adipate) (PBA) during isothermal melt crystallization and phase transition processes is investigated by Fourier transform infrared spectroscopy (FTIR). Detailed IR spectra analysis and band assignment are performed to disclose the bands sensitive to the α-form crystalline order of PBA. It is revealed from the in situ IR study that the functionalities within PBA chains alter simultaneously during the melt crystallization process. From the analysis of the spectral changes, it is found that band shifts take place during the phase transition process of PBA from its metastable β-form crystal to the stable α-form. Notable band shifts in the 1300−1100 cm-1 region indicate that the twist of polymer chains in the α-form is located in the C−O−C and C−O linkages. Moreover, the results elucidated that the different segments of molecular chains tune up their conformations synchronously during the β to α crystal transition process of PBA. It is suggested that the βα phase transition process proceeds randomly throughout the solid at a constant rate.