SILOXANE EQUILIBRATION DURING THE CONDENSATION-REACTIONS OF ORGANOSILICON FUNCTIONAL AMINES AND ANHYDRIDES

The condensation reaction between amines and anhydrides in which one or both of the reactants contain siloxane functionality usually affords imide products in which siloxane redistribution has occurred. The reaction is catalyzed by the amic acid intermediate and prevails when geometry is favorable for intramolecular participation. Poly(imide siloxanes) prepared via this type of condensation process will contain scrambled repeat units in the backbone and will produce cyclic siloxanes as coproducts as a result of the redistribution process. The scrambling can be circumvented by employing imides derived from 2-aminopyridylimides in place of anhydrides in the condensation reaction, thereby avoiding the intermediacy of amic acids. Several examples of siloxane redistribution during the preparation of silicone polyimides are presented. Mechanistic studies derived from model reactions are also presented.