Thermally and Mechanically Enhanced Clay/Polyimide Nanocomposite via Reactive Organoclay

TLDR

The authors synthesized high‑modulus, thermally stable PMDA‑ODA nanocomposites by intercalating montmorillonite with a reactive organoclay formed from p‑phenylenediamine, which first exchanges its onium group with sodium ions in the clay and then covalently bonds to the poly(amic acid) dianhydride, creating irreversible swelling. The resulting nanocomposites exhibited intercalated silicate layers confirmed by X‑ray and TEM, higher glass‑transition and decomposition temperatures, a 2.5‑fold increase in modulus, enhanced maximum stress and elongation‑for‑break, and a 50 % reduction in out‑of‑plane coefficient of thermal expansion compared to pure PMDA‑ODA.

Abstract

High modulus and thermally stable clay/polyimide (pyromellitic dianhydride−4,4'-oxydianiline, PMDA−ODA) nanocomposites were synthesized from reactive organoclay and poly(amic acid). The reactive organoclay was formed by using p-phenylenediamine as a swelling agent for silicate layers of montmorillonite. The swelling process was first carried out through ion exchange between the onium of one amine end group of p-phenylenediamine and the sodium ion in montmorillonite. The other amine end group of p-phenylenediamine reacted with the dianhydride end group of poly(amic acid), producing an irreversible swelling. This irreversible swelling resulted in a nanostructured material containing intercalated nanometer silicate layers dispersed in PMDA−ODA as confirmed by both X-ray and transmission electron microscopy. The glass transition temperature and the thermal decomposition temperatures of this type of clay/PMDA−ODA are higher than that of pure PMDA−ODA. A 2.5-fold increase in the modulus of clay/PMDA−ODA film was obtained as compared to that of pure PMDA−ODA film. Both the maximum stress and the elongation-for-break of these clay/PMDA−ODA nanocomposites increased with the amount of organoclay. The maximum reduction in out-of-plane coefficient of thermal expansion of this type clay/PMDA−ODA was 50% as compared to that of pure PMDA−ODA.