Preparation of carbon membranes from poly ( urethane imide ) and poly-imide copolymers

Pyrolysis of poly ( urethane imide ), polyimide and their copolymer was investigated by FTIR spectroscopy and the resultant carbon membrane was characterized by SEM, nitrogen adsorption and a water flux test. Results indicate that the urethane group is decomposed at 200-300℃ while the imide group is decomposed at 500-700℃. The macropores and micropores are formed during the pyrolysis in the thermally labile urethane component and the thermally stable imide component, respectively. The shrinkage of the polymers during pyrolysis decreases with increasing number of urethane groups or decreasing number of imide groups. The pore size of the carbon membrane can be controlled over a wide range by changing the ratio of imide and urethane components. The addition of carbon black can effectively reduce the shrinkage and apparently increase specific surface area and micropore volume.