Influence of crosslinking technique on the physical and transport properties of ethynyl-terminated monomer/polyetherimide asymmetric membranes

Integrally-skinned asymmetric membranes prepared from blends of polyimides and a reactive monomer were prepared and treated with various energy sources to promote crosslinking. The extent of crosslinking was monitored through differential scanning calorimetry measurements. The influence of crosslinking on the physical and transport properties was measured. Activation procedures included irradiation (UV, γ, and electron-beam) and thermal (at temperatures above and below the glass transition temperature of the polymer). Surface treatment by irradiation resulted in modest improvements in separation selectivity with little reduction in fast gas flux. Limited conversion of the ethynyl moieties was achieved (average<20%). This resulted in negligible improvements in chemical resistance or thermal stability. Irradiation using an electron-beam appears to have lead to polymer chain scission resulting in a reduced thermal stability and glass transition temperature. Thermal treatments resulted in high or complete ethynyl conversion. Complete conversion of the ethynyl units resulted in marked improvements in the resistance to chemicals, thermal stability, and gas selectivity. Because the reaction temperature was higher than the glass transition temperature of the fully reacted blend, collapse of the membrane substructure occurred accompanied by a reduction in membrane permeance. Conversely, thermal treatment at 180°C resulted in a marked increase in the permeance of the membranes with a small reduction in selectivity.