Temperature dependences of gas transport parameters of ladder-like polyphenylsilsesquioxane

The temperature dependences of the diffusion, solubility, and permeability coefficients for ladder-like polyphenylsilsesquioxane (L-PPSQ) samples with molecular weights of 400, 600, and 1000 kDa were analyzed. A comparison, in terms of the gas transport parameters and temperature coefficients, with other silicon-containing polymers revealed that L-PPSQ is most similar to glassy polyvinyltrimethylsilane (PVTMS) rather than to polydimethylsiloxane (PDMS), which is structurally related to it. The heat of sorption values obtained for the studied samples using the temperature dependences are consistent with those from the literature for polytrimethylsilylpropyne (PTMSP), while their diffusion activation energies are more in agreement with PDMS and PVTMS, which may indicate the presence of enclosed free volume elements in L-PPSQ, comparable in size to the ones in PTMSP. The observed tendency of the permeability coefficient to increase with temperature confirms the dominant contribution of the diffusion component of permeability in L-PPSQ. The molecular weight of L-PPSQ was found to have no influence on its gas transport properties in the range of 400–1000 kDa. Therefore, the production of asymmetric and composite membranes is limited solely by the mechanical properties and solubility of L-PPSQ with different molecular weights.