Synthesis and gas transport properties of crosslinked poly(dimethylsiloxane) nanocomposite membranes using octatrimethylsiloxy POSS nanoparticles

• Octatrimethylsiloxy functional group of POSS enhances its dispersion in the polymer matrix.
• Dipole-dipole interaction between POSS and PDMS improves thermal stability of nanocomposites.
• A decomposition mechanism for PDMS-POSS nanocomposites is proposed.
• Membrane selectivities for C3H8/H2, C3H8/CO2 and C3H8/CH4 are improved.
• Nanocomposite membranes are very promising for separation of C3H8 and CO2 from H2 and CH4.

For separation of hydrocarbon compounds from light gases, nanocomposite membranes were prepared by incorporation of polyhedral oligomeric silsesquioxane (POSS) nanoparticles into poly(dimethylsiloxane) (PDMS). First, scanning electron microscopy (SEM) revealed a homogenous dispersion of POSS nanoparticles in PDMS since octatrimethylsiloxy constituents have favorable interactions with the polymer chains. Then, the effect of octatrimethylsiloxy POSS nanoparticles on the thermal stability of the nanocomposite membranes was investigated using thermo-gravimetric analysis (TGA) to propose a decomposition mechanism and discuss the mechanism leading to their increased thermal stability. Thermodynamically, dipole-dipole interaction between POSS and PDMS was found effective to increase thermal stability. Finally, permeability for different gases (H2, C3H8, CO2, and CH4) was measured. The results show that incorporation of only 2% wt. octatrimethylsiloxy POSS in PDMS substantially improved the heat resistance of silicon based membranes with limited reduction in permeabilities for all the gases tested, but C3H8/H2, C3H8/CO2, and C3H8/CH4 selectivities were found to increase.