Soluble, optically transparent polyamides with a phosphaphenanthrene skeleton: synthesis, characterization, gas permeation and molecular dynamics simulations

The present study reports the preparation of five new polyamides from a new diamine monomer, 1,1-bis[2′-trifluoromethyl-4′-(4′′-aminophenyl)phenoxy]-1-(6-oxido-6H-dibenz<1,2>oxaphosphorin-6-yl)ethane, with various aromatic dicarboxylic acids by polycondensation reaction. The polymers were well characterized by different analytical techniques. The polymers were soluble in several organic solvents and showed high thermal stability with 10% weight loss in the temperature range of 345–365 °C in air. Membranes were prepared from these polymers by the solution casting method that showed a tensile strength within the range of 65 to 86 MPa and an elongation at break of 6 to 19% depending on the exact polymer repeat unit structure. The glass transition temperature of the membranes was evaluated by DSC and DMA and the values were within the range of 265–275 °C. The membranes were optically transparent with a cut-off wavelength in the range of 359–396 nm and showed a low dielectric constant. The membranes showed very high gas permeability (PCO2 = 164.7 and PO2 = 59.7 barrer) and offered a good balance of permeability and permselectivity. Molecular dynamics simulations of the polymers were done using an atomistic model that showed good agreement between the size distribution of the free volume and gas transport properties. This study provides an insight into the diffusion behavior of gas molecules in polymer membranes and the results were consistent with the experimentally obtained diffusion behavior.