PERMEABILITY OF SILICONE POLYMERS TO HYDROGEN

Permeability coefficients, PBAR, for H-2 in 10 different types of silicone polymer membranes were measured in the temperature range of 10.0-55.0-degrees-C and at pressures up to 100 psig (approximately 6.8 atm). The values of PBAR decrease slightly with increasing DELTA-p, the pressure difference across the membranes. The permeability of silicone polymers to H-2 increases with an increase in temperature; the values of the energy of activation for permeation are in the range of 1.4-4.3 kcal/mol. The substitution of different functional groups in the backbone and side chains of silicone polymers has similar effects on the permeability of the polymers to H-2 as observed in earlier studies with other light gases. PBAR for H-2 decreases with an increase in the bulkiness of the substituted functional groups. The substitution of Si-O bonds with stiffer Si-C bonds in the backbone chains also results in a considerable decrease in permeability.