The phase transition behavior of poly(butylene adipate) in the nanoporous anodic alumina oxide

PBA nanotubes with different diameters have been prepared. The crystallization behavior and phase transition behavior have been explored by using X-ray diffraction and DSC. For isothermal melt crystallization, the temperature dependence of the crystal phase and the orientation of PBA crystals in the Anodic Alumina Oxide (AAO) templates are very different from that of the bulk. In the AAO templates, especially in the narrow nanopores, the b-axis of the a phase prefers to adopt the orientation parallel to the long axis of the pore. In addition, an in situ X-ray experiment indicates that some molecular chains cannot pack into the crystal lattice in the AAO template at high crystallization temperature, and they are able to crystallize only after cooling back to room temperature. The core-shell structure of PBA exists in the AAO template, which leads to the incomplete crystallization of the a form at higher crystallization temperature and the formation of beta-crystals in the cooled sample. The phase transition behavior of beta-crystals in the heating process is also affected by nanoporous confinement. The expansion of the beta-crystal unit cell is depressed and the phase transition behavior of beta to a is altered in the AAO template. At a slow heating rate, compared to the beta-PBA in bulk, beta-crystals transit to alpha-crystals at a slower rate in the templates. At a fast heating rate, less beta-crystals transit to alpha-crystals and more beta-crystals prefer to melt directly in the AAO templates.