The effect of phenylethynyl terminated imide oligomer molecular weight on the properties of composites

As part of a program to develop high temperature/high performance structura l resins for applications on a Mach 2.4 high speed civil transport, a pheny lethynyl terminated imide oligomer designated PETI-5 has been under investi gation. The oligomer was prepared at a calculated number average molecular weight of about 5000 g/mol and has exhibited good processability and excell ent mechanical properties upon thermal cure at 350-371 degrees 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 mec hanical 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 adhes ive film and unidirectional carbon fiber prepreg. Imide powder of the oligo mers was used for characterization of melt flow behavior and the fabricatio n of neat resin moldings. The PETI-5 oligomers were fabricated into titaniu m adhesive specimens and IM-7 carbon fiber laminates under 0.3-1.4 M Pa for 1 hr at 350-371 degrees 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 sacr ificing toughness (damage tolerance) than the higher molecular weight oligo mer. The neat resin, adhesive and composite properties of the cured polymer s are discussed.