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Polypyromellitimide polymers have been prepared in a two-step process by polymerizing pyromellitic dianhydride with different molar ratios of diisocyanates, toluene 2,4-diisocyanate (TDI) and methylenediphenylene 4,4'-diisocyanate (MDI), in dimethylformamide. Intentionally adding water to the reaction medium to study the effect of adventitious water on the formation of polymer, it was found that the presence of water has an important influence upon the molecular weight of the polymer formed. Moreover, thermal cyclodehydration of polyamic acids results in the corresponding polypyromellitimides. The polymers are characterized by mechanical strength and thermal stability.
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Nien et al. (1997) studied this question.
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