Sorption, swelling and plasticization of PIM-1 in methanol-dimethyl carbonate vapour mixtures

Membranes from PIM-1 represent a promising tool for the efficient recovery of organic components from their vapour mixtures with water or alcohols. To understand the phenomena governing the separation, sorption, swelling and mechanical characteristics were systematically studied for thick PIM-1 films exposed to vapour mixtures of methanol and dimethyl carbonate (DMC). The studied binary vapour mixtures contained 30, 55, 82 and 90 mol.% of methanol and reached 28, 49 and 63 % of the dew point pressure at 40 °C. The separation factor for sorption of vapour mixtures ranged 4.0-7.5, peaked for the azeotropic mixture (82 mol% of methanol) at low saturation (28 % of the dew point pressure), and was significantly contributed by competitive sorption. Furthermore, the tested PIM-1 films exhibited anomalously low volume swelling while their storage modulus remained comparable to that of the pure polymer until exposed to the highly saturated vapours (63 % of the dew point pressure). Raman spectroscopy analysis of PIM-1 swollen by liquid methanol and DMC revealed the pronounced frequency shifts of the C-C vibrations in the aromatic rings and the C-H vibrations in the pentacyclic units. These centres presumably triggered the relaxation of the polymer backbone occurring at high saturations of the vapours. In conclusion, PIM-1 remains highly rigid and selective to DMC in wide ranges of saturation and composition for vapour mixtures of methanol with DMC and is a candidate for effective inversely selective vapour separation membranes.