To prepare clay containing high-temperature processable polymer nanocomposites, new cation exchangeable agents with high thermal stability are required. In this work, we investigated the effect of a thermally stable phosphonium-modified organoclay on the properties of polyimides prepared from the reaction of 4,4′-oxydianiline with 3,3′,4,4′-benzophenonetetracarboxylic dianhydride. The organoclay was prepared from the reaction of pristine clay with octyltriphenylphosphonium bromide. Phosphonium-modified clay displayed a negligible weight loss (<5%) below 300°C. The thermal stability of the composites enhanced with the increasing amount of phosphonium-modified clay. [ABSTRACT FROM AUTHOR]