Aromatic imide polymers for high‐temperature adhesives

Abstract

AbstractDuring the past decade the aerospace industry has sought materials for bonding stainless‐steel and titanium alloys that have a high degree of thermal and oxidative stability. The Air Force Materials Laboratory has anticipated these requirements and sponsored many development programs aimed at achieving these goals. This paper describes the results of one such program devoted to development of high‐temperature adhesives from aromatic imide polymers. The family of polymeric materials known as aromatic polyimides possess excellent thermal and oxidative resistance at temperatures up to 650°F. Mechanical and electrical properties of glass‐fiber‐reinforced laminates prepared with these polymers have been reported. This work has been extended to the development of structural adhesives that will withstand long‐time exposure in air at 600°F. Stainless steel and titanium have been successfully bonded with adhesives made from aromatic imide and benzimidazole imide polymers. Bonds made with stainless steel have retained approximately 80% of their original strength at 600°F. after 1000 hr. of aging at 600°F. Adhesives made with benzimidazole imide polymers are the prepared materials for bonding titanium. Initial bond strengths of 1300 psi have been measured at 600°F. After 1000 hr. at 600°F. the bond strengths drop to 800 psi. The processing conditions for making a bond are quite moderate, except that a high temperature is required. The preparation and processing conditions associated with these adhesives are described. A large number of aromatic imide and amide‐imide polymers have been prepared and adhesives formulated. By comparing the bond strengths obtained with these adhesives it is possible to deduce the effect of molecular weight and various molecular components on bond strength.