Structure-stability correlation of copolyimide membranes derived from aliphatic/alicyclic/aromatic diamine and aromatic dianhydrides
Abstract
New polyamic acids with -A-B-A-C- type periodic sequence of monomeric units (A derived from a diamine, B from benzophenone-3,3,4,4-tetracarboxylic dianhydride, and C from benzene-1,2,4,5-tetracarboxylic dianhydride) are prepared and transformed into polyimide membranes that are examined by various methods in order to investigate the influence of diamine units (aliphatic, alicyclic, or aromatic) on the morphology, thermal stability, and mechanical properties of membranes. Small- and wide-angle X-ray scattering and Atomic force microscopy show amorphous character of all membranes except for those containing hexane-1,6-diamine units.
Thermogravimetric analysis reveals a decrease in the initial decomposition temperature from 551/501 degrees C to 437/395 degrees C (for N-2/O-2 atmosphere) when going from membranes with aromatic to those with aliphatic diamine units. Dynamic mechanical analysis shows quite high initial storage modulus (2100-3300 MPa) for all membranes at frequencies of 1, 10, and 20 Hz.
The properties of prepared copolymeric polyimide are promising for a wide range of their potential technological applications.