Poly(dimethylsiloxane-urethane) membranes: effect of linear siloxane chain and caged silsesquioxane on gas transport properties

The effect of poly(dimethylsiloxane) (PDMS) or polypropylene glycol (PPG) linear chain and polyoctahedral oligosilsesquioxanes (POSS) cubic nanoparticles on surface and gas transport properties of poly(dimethylsiloxane-urethane) PDMS-PU or poly(propylene glycol-urethane) (PPG-PU) hybrid membranes were studied. PDMS-PU or PPG-PU hybrid membranes were prepared using PDMS-diol or PPG-diol as a chain extender and diisocyanate with POSS-amine macromonomer as a crosslinker. The macromer synthesized was characterized using FT-IR, 1H-, 13C- and 29Si-NMR spectroscopic methods. The hybrid membranes were characterized by CP-MAS 29Si-NMR, DSC, contact angle, WAXD, AFM and density measurements. The glass transition temperature (Tg) of the hybrid membranes were determined by differential scanning calorimetry (DSC) and were found to be in the range of 176–189°C. The surface free energy was reduced by increasing the POSS-amine crosslinker content of the membranes. The AFM measurement showed phase separation of POSS-amine molecule and PDMS with the urethane matrix on the surfaces. The XRD profiles confirm that the membranes were highly amorphous in nature. The decrease in permeability was observed by increasing the concentration of POSS-amine incorporated hybrid membranes. The selectivities of O2/N2 and CO2/N2 gas pairs increased with an increase in the POSS concentration. This suggests that the selectivities were dependent mainly on the presence of urethane and ester functional groups in the crosslinker.