Synthesis and thermal, mechanical and gas permeation properties of aromatic polyimides containing different linkage groups

Two series of aromatic polyimides containing various linkage groups based on 2,7-bis(4-aminophenoxy)naphthalene or 3,3'-dimethyl-4,4'-diaminodiphenylmethane and different aromatic dianhydrides, namely 4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride), 4,4'-(hexafluoroisopropylidene)bis(phthalic anhydride), 3,3',4,4' benzophenonetetracarboxylic dianhydride, 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride and 4,4'-(4,4'-hexafluoroisopropylidenediphenoxy)bis(phthalic anhydride), were synthesized and compared with regard to their thermal, mechanical and gas permeation properties. All these polymers showed high thermal stability with initial decomposition temperature in the range 475-525°C and glass transition temperature between 208 and 286°C. Also, the polymer films presented good mechanical characteristics with tensile strength in the range 60-91 MPa and storage modulus in the range 1700-2375 MPa. The macromolecular chain packing induced by dianhydride and diamine segments was investigated by examining gas permeation through the polymer films. The relationships between chain mobility and interchain distance and the obtained values for gas permeability are discussed.