Polysiloxanes with pendent bulky groups having amino-hydroxy functionality: Structure–permeability correlation

A series of poly(dimethylsiloxane) (PDMS) films substituted with different bulky groups in the pendent chain having amino and hydroxy functional groups have been prepared. FT-IR, 1H- and 13C NMR, GPC, TGA, DSC and WAXD techniques were used to characterize the products. The gas transport properties, viz., permeability, solubility and diffusivity, of the functionalized PDMS films were determined for N2, O2, CH4 and CO2 gases. With the incorporation of increasingly bulkier substituents the permeability coefficient was found to decrease. The decrease in value was observed to be low compared to other reported bulky substituents. The glass transition temperature increases with increasing bulkiness of the substituent. The fractional free volume (FFV) and d-spacing values were also determined and correlated with the permeability coefficients. The permselectivity of these films for O2/N2 and CO2/CH4 gas pairs increases due to increase in the solubility selectivity value. Among these, the PDMS film functionalized with 2,6-diisopropyl phenyl amino-hydroxy groups shows high permselectivity value for the studied gas pairs without much reduction in the permeability value.