Effect of Chain Extender Length on Gas Permeation Properties of Polyurethane Membranes

The effects of chain extender length on the gas permeability of polyether-based polyurethanes were investigated. Synthesized polyurethanes were based on 1000 and 2000 molecular weight polytetramethylene-glycol (PTMG) with toluene diisocyanate (TOI). Ethylene glycol, 1A-butane diol (BOO), 1,6-hexane diol (HOO) and 1,1O-decane diol (000) chain extenders were used to complete the conversion of prepolymers to the final polyurethanes . Membranes made from polyurethane were used to study the permeability and diffusivity of nitrogen, oxygen, methane, and carbon dioxide. Lag time method was used to determine the diffusivity of gases in polyurethanes. This study indicated that glass transition temperature of the polymers decrease by chain extender s length. The increase in chain extender s length makes the phase separation more probable. OSC and FTIR studies also indicate the extent of the phase separation in polyurethanes. Permeability and diffusivity of gases increase with the increasing length of the chain extenders. Selectivity of CO2/N2 changed by chain extender length, while selectiv ity of CO2/CH4 and 02/N2 did not show any remarkable changes. This study shows that solubilization is the dominant mechanism in gas permeation process in polyurethane membranes.