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Polyimide structure–property relationships. II. Polymers from isomeric diamines

1976; Wiley; Volume: 14; Issue: 9 Linguagem: Inglês

10.1002/pol.1976.170140917

1542-9369

Vernon L. Bell, B. L. Stump, H. M. Gager,

Epoxy Resin Curing Processes

Abstract An extensive study of the effects of stereoisomeric variations in aromatic polyimide structures on polyimide properties was conducted. The structural variations were incorporated into the polyimides through the use of two complete series of isomeric aromatic diamine monomers, the diaminodiphenylmethanes and the diaminobenzophenones, as well as several pairs of diamine isomers. The ability of the diamines to polymerize was related to the basicities, and thus reactivities, of the amino groups. Diamines with an amino group located ortho to the group connecting the two aromatic rings were successfully polymerized with dianhydrides for the first time to high molecular weight poly(amic acids). The stereoisomeric polyimides were characterized by determining the glass transition temperatures T g , mechanical properties, and thermooxidative stabilities of thin films of the polymers. The polymers prepared from p ‐diamines were shown to have the highest softening points and thus, the most rigid molecular structures. Those synthesized from m ‐diamines had the lowest T g values, inferring the most flexible molecular backbone. With limited exceptions, the use of diamines with ortho ‐oriented amine groups failed to improve the flexibility of the polyimides since their T g values were usually as high as those of polymers made from p ‐diamines. Only slight differences in mechanical properties of the isomeric polyimide films were attributable to the variations in isomeric structure, except for those properties dependent upon T g changes, such as elevated temperature mechanical properties. A study of the thermooxidative stability of the polyimides showed little difference between the polymers prepared from the diaminobenzophenones, but marked differences were observed between the individual members of the diaminodiphenylmethane‐derived polyimides.