Polysiloxaneimide membranes: Gas transport properties

A polysiloxaneimide (PSI) membrane was prepared for studies of gas (O-2/N-2) separation. The effect of introducing siloxane into a polyimide backbone to enhance the gas permeability of polysiloxaneimide membrane was studied. This polysiloxaneimide (PSI) polymer wits prepared by condensation of pyromellitic dianhydride (PMDA), 4,4'-oxydianiline (ODA) and amine-terminated poly(dimethyl siloxane) (PDMS). The effects of PDMS content on membrane morphology were measured by X-ray diffraction. It was found that the PDMS content played an important role in the packing of PSI polymer chains. The effects of the membrane composition on the gas permeability and O-2/N-2 selectivity were measured at 35, 65, 95 and 125 degrees C at a pressure drop of 1 atm and the operating upstream pressure was increased from 1 atm up to 9 atm at 125 degrees C. If the diffusion-solution model was adopted, the increase in PDMS content greatly increased the gas permeability and the gas diffusivity. It was found that when the PDMS content was higher than 20 wt% the gas separation mechanism was dominated by diffusion rather than gas solubility. Copyright (C) 1996 Elsevier Science Ltd