Direct Formation of γ Form Crystal of Syndiotactic Polystyrene from Amorphous State in Supercritical CO₂

Abstract

The crystallization behavior of amorphous syndiotactic polystyrene (sPS) in supercritical CO2 was investigated in detail by using wide-angle X-ray diffraction, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The pure γ form crystal was obtained directly after treating amorphous sPS in supercritical CO2 in a range from 8 to 20 MPa and from 35 to 100 °C. This transformation in supercritical CO2 was accelerated by increasing temperature. Supercritical CO2 provided a moderate condition to crystallize the amorphous into the γ form, while liquid CO2 could not induce the γ form even at the pressure as high as 20 MPa.

Supercritical Fluid Assisted Crystal Transition of γ‐Form Crystal in Syndiotactic Polystyrene

“…Furthermore, the presence of CO 2 can bring about some new transitions that cannot occur under ambient pressure. Phase transitions of sPS in the presence of CO 2 have been reported by Handa et al [18] and He et al [21,22] The phase transition of the g-form sPS to the a form occurred at lower temperature in compressed CO 2 than those under ambient pressure. [18] In the presence of CO 2 of 57 atm, the Summary: In different media in the range of approximately 160-240 8C, the g form of syndiotactic polystyrene was transformed into different crystal forms having different stabilities.…”

“…The sample exhibits the typical characteristics of the g form (2 y ¼9.2, 10.3, 16.0, 20.0, 28.38), [5,18,22] which suggests that the polymer chains in amorphous sPS samples are rearranged into the g form with the helical conformation as a result of the increased molecular mobility in the presence of supercritical CO 2 . [22] Subsequently, the g-form samples are treated further under different conditions to study the crystal transition behaviors of the g-form sPS. The thermal conditions for treating g-form samples are summarized in Table 1.…”

“…[22] Briefly, a high-pressure apparatus was used for the treatment in CO 2 . The amorphous sPS samples were loaded into a 25-mL high-pressure vessel which was then flushed with low-pressure CO 2 for about 2 min.…”

Supercritical CO2 induced phase transition of Form III in isotactic poly‐1‐butene

“…[27] The solid-solid phase transition of sPS under supercritical CO 2 has been widely reported. [35,36] The special interaction between supercritical CO 2 and the polymer chains significantly influences the polymer structure and the conformation. [32] Thus, the phase transition of iPB-1 Form III under supercritical CO 2 must be different from those without it.…”

Process analysis of phase transformation of α to β-form crystal of syndiotactic polystyrene investigated in supercritical CO2

“…Not only the crystallization process of polymers from melt and glassy state, but also the phase transition between different crystal forms is influenced in the presence of high pressure CO 2 . Up to now, most the works about phase transition under CO 2 are proceed in sPS system [34,43,44]. However, the relationship between the effect of the existing b form and the phase transformation has not been investigated in supercritical CO 2 , even though most of the factors controlling the crystallization of a and b forms at ambient pressure have been clarified.…”