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

Abstract

Polyimide alloys are prepared by blending the crosslinked and uncrosslinked polyamic acid components and followed by thermal imidization. The blend components can be synthesized by the reaction of polyamic acid with the varying concentration of crosslinker [here methylene bis (4‐phenyl isocyanate or MDI)] from 1.54 × 10−2 mol/L (i.e. hypothetically calculated critical crosslinker concentration or CCC) to 1.54 × 10−6 mol/L. This communication discusses the synthesis and characterization of polyimide (PI) blends and alloys prepared by varying degrees of crosslinking introduced via isocyanate‐amic acid reaction. The polyimides were prepared by thermally imidizing the polyamic acid blends at different curing temperatures from 50°C to 350°C. The degree of imidization and residual solvent content for blends having varying mole fractions of crosslinked (or branched) and uncrosslinked components and two extreme conditions and at specified temperature‐time profiles have been studied. The resultant PI‐MDI blends have exhibited synergism on mechanical properties. The improvement in mechanical properties, however, was significantly higher at the lower imidization temperature (i.e. 50°C to 150°C). The feasibility of preparing polyimide alloys with synergistic combinations of crosslinked and uncrosslinked polyimide components was inferred.

In situ generated hydroxyl‐terminated polybutadiene nanoparticles in polyimide films

“…The nature and numbers of chain ends influence the rate and extent of thermal decomposition of HTPB. 13 Hence, at elevated temperature the principle effect of the hydroxyl end groups in HTPB is not to accelerate the depolymerization but to assist the saturation of C C double bonds leading to enhanced thermal stability along with better mechanical properties of the cured PHB films. Curing of PHB films at 350…”

“…Methanol was chosen as an extracting solvent for the removal of residual DMAc. 1,12,13 The dried and weighed films were dipped in methanol and the films were weighed after every 24 h. After 72 h the films were dried at 110…”