SYNTHESIS AND CHARACTERIZATION OF POLYIMIDES FROM 3,7-DIAMINOPHENOTHIAZINIUM CHLORIDE (THIONINE)

A new series of thermally stable, organic solvent soluble polyimides h as been synthesized by reacting the tricyclic heterocyclic molecule 3, 7-diaminophenothiazinium chloride, thionine, with four different dianh ydrides. With the exception of the polyimide obtained from pyromelliti c dianhydride and thionine, the polyimides were synthesized by a singl e-stage polymerization reaction at an elevated temperature. For these polymers, the conditions necessary for the polymerization to proceed d id not permit the isolation of the intermediate poly(amic acid). To as sess the reactivity of the primary amine groups of the thionine molecu le, model compounds were prepared by reacting thionine with phthalic a nhydride. This reaction was studied in different solvents and under va rious experimental conditions so that the intermediate diamic acid cou ld be isolated. Subsequent treatment of the bis(phthalic diamic acid) at elevated temperatures yielded the bis(phthalic diimide). The polyim ides obtained from thionine and the dianhydrides 3,3',4,4'-benzophenon e tetracarboxylic dianhydride (BTDA) and 4,4'-(hexafluoroisopropyliden e) diphthalic anhydride (6FDA) were soluble in many of the common orga nic solvents, whereas the polyimides obtained from the dianhydrides py romellitic dianhydride (PMDA) and naphthalenetetracarboxylic dianhydri de (NTCDA) were soluble in fewer organic solvents but dissolved comple tely in strong acids without decomposition. The differences in solubil ity of these polyimides are attributed to the differences in the dianh ydride flexibility and polarity. Differential thermal analyses and the rmogravimetric studies established that these polyimides were thermall y stable up to 500-degrees-C in air. The polyimides prepared with pyro mellitic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydr ide, or 1,4,5,8-naphthalenetetracarboxylic dianhydride exhibited a 10% weight loss in the region of 507-degrees-C in air. The polyimide synt hesized with 3,3',4,4'-benzophenonetetracarboxylic dianhydride exhibit ed a 10% weight loss at 539-degrees-C in air. All four polyimides exhi bited improved thermal stability ranging from 10 to 80-degrees-C in a nitrogen atmosphere. Characterization of the polyimides by X-ray diffr action showed that the polyimide obtained from thionine and PMDA had a greater degree of crystallinity than the other polyimides. Computer s imulations of the geometry of each polyimide indicated a preference by that polyimide for its own unique helical structure conformation.