The Effect of Phenylethynyl Terminated Imide Oligomer Molecular Weight on the Properties of Composites

Abstract

As part of a program to develop high temperature/high performance structural resins for applications on a Mach 2.4 high speed civil transport, a phenylethynyl terminated imide oligomer designated PETI-5 has been under investigation. The oligomer was prepared at a calculated number average molecular weight of about 5000 g/mol and has exhibited good processability and excellent mechanical properties upon thermal cure at 350-371°C for 1 hr. However in the fabrication of complex composite structures, primarily skin stringer structure, a resin with improved flow and equivalent or better mechanical properties was desired. To improve melt flow (i.e., processability or compression moldability), 1250 and 2500 g/mol molecular weight versions of PETI-5 were prepared and their solutions used to prepare supported adhesive film and unidirectional carbon fiber prepreg. Imide powder of the oligomers was used for characterization of melt flow behavior and the fabrication of neat resin moldings. The PETI-5 oligomers were fabricated into titanium adhesive specimens and IM-7 carbon fiber laminates under 0.3-1.4 MPa for 1 hr at 350-371°C. The lower molecular weight oligomers exhibited improved processability, and when cured, higher T g s and better retention of mechanical properties at elevated temperature without significantly sacrificing toughness (damage tolerance) than the higher molecular weight oligomer. The neat resin, adhesive and composite properties of the cured polymers are discussed.