Empty δ Crystal as an Intermediate Form for the δ to γ Transition of Syndiotactic Polystyrene in Supercritical Carbon Dioxide

Abstract

The crystal transition behavior of δ form syndiotactic polystyrene (sPS) in supercritical CO2 was investigated in detail by using Fourier transform infrared spectroscopy and differential scanning calorimetry. The empty δe form sPS was obtained after treating the δ form in supercritical CO2 of 12 MPa in a range from 35 to 80 °C. At higher temperatures, the δ form transformed into the δe form transiently and then into the γ form. The existence of the intermediate δe form lowered the temperature for the δ to γ transition. At 240 °C, supercritical CO2 of 12 MPa transformed the δ crystal form into more stable β form without passing through the δe form. Increasing the pressure of supercritical CO2 made the δ to δe transition occur easily and decreased the temperature for the δ to β transition.

Understanding at molecular level of nanoporous and co-crystalline materials based on syndiotactic polystyrene

“…Although, as usual, hopping events are facilitated by transient channels of free volume between existing cavities and the channels are formed by thermal motions of the host polymer atoms [83][84][85][86], for a nanoporous crystal phase average sizes and locations of the cavities, as well as crystallographic directions of the channels, are all identical. Several recent experimental studies have shown the additional ability of s-PS, possibly unique for polymer films, to be formed with three different kinds of orientation of the helical crystalline phase [13,[87][88][89][90].…”

“…MD simulations techniques have been used to understand the diffusive behavior of helium and CO 2 in the crystalline phase of s-PS and particularly its anisotropy, also as a function of temperature [83,84]. The diffusion of CO 2 is particularly relevant because, at present, extraction procedures by CO 2 represent the most efficient way to remove guest molecules from s-PS co-crystalline phases and regenerate the nanoporous d and e phases [21,85,86]. The main advantage of the simulations is that a well-defined and purely crystalline system can be studied, whereas the experiment has to cope with semicrystallinity (i.e.…”

Microporous-crystalline microfibers by eco-friendly guests: An efficient tool for sorption of volatile organic pollutants

“…The complete removal of EA (boiling point = 77 °C) from the same 3 µm fibers requires, instead, extraction procedures by liquid acetonitrile [27,46] or by supercritical CO 2 [47][48][49]. Table 1.…”

Factors controlling the structure of syndiotactic polystyrene upon the guest exchange and guest extraction processes

“…Many authors have been reported the formation of these nanoporous-crystalline phases (δ e and ε e ) by suitable guest extraction procedures using the volatile solvents like acetone [14,41,71], acetonitrile [15,16,43], or supercritical carbon dioxide [69,70]. It was reported that guest removal from the δ clathrate and intercalate leads to the formation of the δ e form.…”