In-situ high-pressure FTIR was used to investigate the polymorphous phase transition of isotactic poly-1-butene (iPB-1) with form III upon annealing at temperatures ranging from 75 to 100 degrees C and CO2 pressures ranging from 2 to 12 MPa. It was shown that the phase transition of form III changed from form III toll not through form III to I with increasing temperature and application of CO2 increased the content of generated form I'. Wide-angle X-ray diffraction (WAXD) measurement on the annealed iPB-1 with form III verified the phase transition of form III. The crystalline morphology of the annealed iPB-1 films was investigated using polarized optical microscopy (POM). The results implied that the phase transition of form III to I' might process via a solid-solid transition, which did not affect the orientation of the lamellar stacks. The orientation of form II lamellar stacks depended strongly on the formation process. To obtain strong orientation, the formation process displayed the following order: melt crystallization at ambient condition > melt recrystallization under CO2 > phase transition upon annealing at ambient condition. Avrami equation could be well established to describe the phase transition of form III to I' through a solid solid phase transition. (C) 2011 Elsevier Ltd. All rights reserved.