Physicochemical characterization of alloy of polyimide with varying degreeof crosslinking through diisocyanates

Polyimide alloys are prepared by blending the crosslinked and uncrosslinked polyamic acid components and followed by thermal imidization. The blend co mponents can be synthesized by the reaction of polyamic acid with the varyi ng concentration of crosslinker [here methylene bis (4-phenyl isocyanate or MDI)] from 1.54 x 10(-2) mol/L (i.e. hypothetically calculated critical cr osslinker concentration or CCC) to 1.54 x 10(-6) mol/L. This communication discusses the synthesis and characterization of polyimide (PI) blends and a lloys prepared by varying degrees of crosslinking introduced via isocyanate -amic acid reaction. The polyimides were prepared by thermally imidizing th e polyamic acid blends at different curing temperatures from 50 degrees C t o 350 degrees C. The degree of imidization and residual solvent content for blends having varying mole fractions of crosslinked (or branched) and uncr osslinked components and two extreme conditions and at specified temperatur e time profiles have been studied. The resultant PI-MDI blends have exhibit ed synergism on mechanical properties. The improvement in mechanical proper ties, however, was significantly higher at the lower imidization temperatur e (i.e. 50 degrees C to 150 degrees C). The feasibility of preparing polyim ide alloys with synergistic combinations of crosslinked and uncrosslinked p olyimide components was inferred.