Preparation, structure, properties and thermal behavior of rigid-rod polyimide/montmorillonite nanocomposites

Polyimide/montmorillonite nanocomposites were prepared from solution of pol y(amic acid) precursors and the dodecyl-montmorillonite (DMONT) using N-met hyl-2-pyrrolidone as a solvent. The cured films of the rigid-rod polyimide/ DMONT hybrids as characterized by FTIR, TEM and WAXD were exfoliated nanoco mposites at low DMONT content ( <1 wt.%) and partially exfoliated nanocompo sites at high DMONT content (containing aggregates of DMONT). The nanocompo site showed optimum properties at 3 wt.% DMONT with low water absorption, i mproved mechanical strength and modulus, and high dielectric strength. The clay content significantly influences thermal behavior of the nanocomposite films, such as thermal expansion coefficient (CTE), glass transition and y ielding temperatures of the rigid-rod and flexible polyimide nanocomposites . It was found that the rigid polyimide matrix gave a superior thermal beha vior; i.e. lower CTE, higher glass transition and yielding temperatures tha n the flexible ones. Effect of DMONT content was significant at high temper ature operation where a side reaction of dodecylamine and a poly(amic acid) should he aware to cause a reduction in degree of imidisation and glass tr ansition temperature and the formation of silicate layer aggregates. High D MONT content nanocomposites (aggregates were formed) showed high yielding t emperatures indicating the suppression of polymer flow by the rigidity of t he clay. The flexible polyimide nanocomposites showed higher thermal deform ation than the rigid ones. Moreover, the rigid polyimide nanocomposite with 9 wt.% DMONT showed a thermally reversible behavior indicating that the si licate layers efficiently suppressed the deformation of the rigid polyimide . (C) 2001 Elsevier Science Ltd. All rights reserved.