Nonstoichiomeric polymerization of polyimide by using reaction-induced crystallization of oligomers

Nonstoichiometric preparation of poly(4,4'-oxydiphenylene pyromelliteimide)(Kapton) from pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) was examined by using reaction-induced crystallization of oligomers. When the polymerization was carried out under stoichiometric condition, the crystals having η_inh of 1.58 dL/g were obtained. Under the excess ODA, η_inh was insensitive toward the imbalance of stoichiometry, and suprisingly, η_inh became 1.63 dL/g even under 50 mol% excess. In the polymerization under nontoichiometric condition, the terminated oligomers precipitated to form the crystals and the solid-state polymerization proceeded with the elimination of terminated oligomer unit in oligomer crystals resulting in high molecular weight.