Structure–Property Relationships of Random Aromatic Copolyamide Membranes by the Partial N‐Methylation of Amide Linkages

Abstract

The internal and surface structures and transport properties of partially N‐methylated aromatic random copolyamides are reported. The results from positron annihilation lifetime spectroscopy demonstrate that the N‐methylation of the amide linkages in the polymer backbone increases the size of the free volume in the membrane. The time‐resolved water contact angle measurements also indicate that the N‐methylation of the amide linkages increases the chain mobility at the membrane surfaces and consequently enhances the water‐induced surface reorganization. The partial N‐methylation of aromatic copolyamides can be used to control the internal and surface structures of the membranes. In particular, the size of the free volume can be tuned by suppressing the hydrogen bonding between the polymer chains, improving the transport properties through the membranes.