Controlling the structure and rheology of polyimide/nanoclay composites by condensation polymerization

Abstract

Abstract A novel in situ condensation polymerization method for controlling the structure and dispersion of clay in the polyimide (PI) matrix has been investigated. Initially, the viscosity of the polymerizing poly(amic acid) (PAA) solution increases rapidly with increasing shear rate and polymerization time. In the presence of clay, the PAA solution viscosity became significantly higher than that for the neat PAA solution at initial polymerization stage; however, it attained a final value, which was significantly lower than that for a neat PAA solution after a long polymerization time. The PAA/clay solution synthesized by in situ polycondensation reaction also showed an interesting optical activity between 500 and 600 nm. The PAA/clay solution prepared by a two‐step method involving polymerization followed by the addition of clay shows no unusual optical behavior above 400 nm. The imidization of PAA is enhanced in the presence of clay. The imidization temperature decreased significantly in the presence of clay, and the extent of imidization increased with increasing amount of clay and cure temperature. X‐ray diffraction and microscopy studies show the existence of exfoliated clays at low concentration of clay and at high curing temperatures. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012