Controlling crystal phase transition from form II to i in isotactic poly-1-butene using CO_2

摘要

Controlling crystal phase transition from modification II to I in isotactic Poly-1-butene (iPB-1) using CO_2 is presented in this article. The intrinsic kinetics of CO_2-induced phase transition from modification II to I in iPB-1 at 40°C and different CO_2 pressures were detected using in situ high-pressure Fourier transform infrared spectroscopy (FTIR) and correlated by Avrami equation. Sorption of CO_2 in iPB-1 matrix was measured at 40°C and different CO_2 pressures using both FTIR and magnetic suspension balance (MSB) and the diffusivity was determined by Fick's second law. An algorithm combining the CO_2 diffusion and induced phase transition was subsequently proposed to calculate the CO_2 concentration as well as the phase transition degree in the iPB-1 matrix with different thickness at different saturation time. The calculated phase transition degree in the iPB-1 agreed well with the FTIR results. In addition, the yield stresses of iPB-1 specimens annealed in the air and 6 MPa CO_at 40°C with different durations were also experimentally investigated. The algorithm was applied to predict the phase transition degree of the iPB-1 specimens. The appropriate CO_2 treatment time for getting high yield stress was in consistent with that predicted by the algorithm.