Synthesis, characterization, and gas permeation properties of silylated derivatives of ethyl cellulose

Silyl ethers of ethyl cellulose (2a-f) were synthesized in good yields by the reaction of various chlorosilanes with residual hydroxy groups of ethyl cellulose. H-1 NMR and FTIR spectra of the silylated polymers furnished the evidence for complete substitution of hydroxy protons by the silyl groups. Silylated derivatives of ethyl cellulose (2a-f) were soluble in common organic solvents and displayed enhanced solubility in relatively nonpolar solvents due to the substitution of hydroxy groups. The onset temperatures of weight loss of the silylated derivatives (2a-f) in air were higher than 270 degrees C, indicating fair thermal stability. Free- standing membranes of 1 and 2a-f were fabricated by casting their toluene solution, and all the silylated derivatives (2a-f) exhibited enhanced gas permeability ( P) as compared to that of ethyl cellulose ( 1). An increment in the size of the silyl group led to the decrement in gas permeability of the polymers, and trimethylsilyl derivative (2a) exhibited the highest P value. The P-CO2/P-N2 permselectivity values of the polymers (2a-f) were observed to be in the range of 15-19. The data for 2a, 2b, and 2c were located above Robeson's upper bound, in the plot of permselectivity vs permeability for the CO2/N-2 gas pair (PCO2 vs PCO2/PN2). Gas diffusion coefficients ( D) increased upon silylation for all the six gases under study, while gas solubility coefficients ( S) underwent a decline.