ИСТИНА

Thermal rearrangement of membrane materials has become one of the modern trends to improve their transport properties. In particular it was made for low permeable polyimide (PI). A gap in current knowledge regarding the reason for increases in gas permeability of such materials is the absence of the data on their sorption capacity and other thermodynamic properties. Thus, the aim of this work was to investigate Inverse Gas Chromatography (IGC) the infinite dilution sorption of n-alkanes C7-C16 in original polyimide with hydroxylgroups (HPI) and its thermally rearranged product (TR) polybenzoxazole. The original polymer was deposited on a macroporous support Inerton AW (0.16-0.20 mm) from its tetrahydrofuran solution (5 wt.%). The weight fraction of the polymer on the inert support was 9.3±0.1%. A half of the dried ‘sorbent’ was then heated according to the thermal treatment protocol used previously [1] (heating (5°C/min) up to 300°C, keeping for 1hr at this temperature, heating (5°C/min) up to 450°C, keeping for 1hr at this temperature and cooling to the ambient temperature) in an inert atmosphere of nitrogen. Sorption of n-heptane and n-octane in the original HPI was studied on a gas chromatograph with flame ionization detector in the temperature range 60-90°C whereas sorption of n-C7, n-C8, n-C10, n-C12, n-C14 and n-C16 solutes in TR polymer was investigated in the range 195-280°C. The rate of carrier gas (helium) was maintained at 5.0±0.2 cm3/min over all experiments. Retention diagrams (Fig. 1) of all the solutes in the both polymers were linear which indicated indirectly the absence of diffusion limitations during the IGC experiments. Extrapolation of the temperature dependencies of specific retention volume (Vg on Fig. 1) to 35°C allow us to calculate solubility coefficients of the solutes.