Abstract
In order to clarify the thermal cyclization mechanism for the introduction of isoindoloquinazolinedione(IQ) unit in the backbone of polyimides, three model compounds I, II and III of poly(b iphenylphthalic dianhy decide -oxy dianiline-4,4'-diamino -3'-carbamoylbenzanilide)(Poly(BPDA-ODA-DACB)) have been synthesized. It has been found that two possible mechanisms are operating during the structural change by heat treatment of the model compound; one is the formation of quinazolone ring first, i.e. the compound IV, followed by the formation of IQ unit, i.e. the compound VI, and the other is the formation of imide ring, i.e. the compound V, precedes the formation of IQ ring structure, i.e. the compound VII, which finally transforms to more stable IQ structure, i.e. the compound VI on further heat treatment at high temperatures. It tuns out that a gradual heat treatment favors the second reaction mechanism.