Preparation and characterization of polyimide/organoclay nanocomposites

Organically modified montmorrillonite clay, containing a long chain aliphat ic quarternary ammonium cation, was used to prepare polyimide/organoclay hy brids. Several approaches were examined in an attempt to achieve fully exfo liated nanocomposites. These included simple mixing of the clay in a pre-ma de high molecular weight poly(amide acid) solution; simple mixing followed by sonication of the organoclay/poly(amide acid) solutions; and the prepara tion of high molecular weight poly(amide acid)s in the presence of the orga noclay dispersed in N-methyl-2-pyrrolidinone (NMP). The best results were o btained using the in-situ polymerization approach. The resulting nanocompos ite films (both amide acid and imide), containing 3-8% by weight of organoc lay, were characterized by differential scanning calorimetry (DSC), dynamic thormogravimetric analysis (TGA), transmission electron microscopy (TEM), X-ray diffraction (XRD) and thin film tensile properties. A significant deg ree of dispersion was observed in the nanocomposite films of the amide acid and the imide. After thermal treatment of amide acid films to effect imidi zation, in both air and nitrogen, the films were visually darker than contr ol films without clay and the level of clay dispersion appeared to have dec reased. In the latter case, the separation between the layers of the clay d ecreased to a spacing less than that present in the original organoclay. Th ese observations suggest that thermal degradation of the aliphatic quartern ary ammonium cation occurred likely during thermal treatment to effect imid ization and solvent removal. These thermal degradation effects were less pr onounced when thermal treatment was performed under nitrogen. The polyimide /organoclay hybrid films exhibited higher room temperature tensile moduli a nd lower strength and elongation to break than the control films. (C) 2001 Elsevier Science Ltd. All rights reserved.