Synthesis and characterization of new water-soluble precursors of polyimides

We have successfully synthesized and characterized new water-soluble precursors of polyimides based on dianhydrides with diaminobenzene sodium sulfonate (DABSS) and diaminostilbene disodium sulfonate (DASBDSS). The precursors are soluble in water and methanol as well as in several aprotic solvents. The optimum inherent viscosities of the poly(amic acids), obtained by varying reaction temperatures, were measured using a conventional Ubbelohde viscometer. The average molar mass of the polymers expressed as the ''poly(ethylene oxide)-PEO/poly(ethylene glycol)-PEG equivalent'' molecular masses obtained by gel permeation chromatography (GPC) showed significant broad molecular mass distributions with their polydispersities ranging from 2.9 to 4.6. FT-IR spectra revealed complete imidization of the polyimides. Their thermal properties were studied by techniques such as differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Polyimides derived from the dianhydrides and DASBDSS showed better thermal stability up to 40 degrees C in nitrogen than In oxygen atmosphere. However, polyimides based on the dianhydrides and DABSS were slightly more stable in oxygen than in nitrogen atmosphere. In oxygen, all the synthesized polyimides exhibited weight losses of about 50% in the range of 450-510 degrees C. The overall weight losses of these polyimides under nitrogen were less than 50% at 700 degrees C. New network polymellitimides based on mellitic trianhydride (MTA) and DABSS, and co-polymellitimides based on MTA, DABSS, and ODA (oxydianiline) were also synthesized and characterized successfully. Their thermal stabilities were compared with the linear polyimides using TGA and DSC.