Imide oligomers containing pendent and terminal phenylethynyl groups

Abstract

As part of a programme to develop high performance/high temperature structural resins for aeronautical applications, imide oligomers containing pendent and terminal phenylethynyl groups were prepared, characterized and the cured resins evaluated as adhesives and composite matrix resins. As a means of controlling the molecular weight between reactive sites (i.e. crosslink density), varying amounts of phenyl-ethynyl groups were distributed randomly along the imide oligomer whose calculated number-average molecular weight was 5000 g mol−1. Upon thermal cure at 350–371°C for 1 h in air, the phenylethynyl group undergoes a complex reaction resulting in chain extension, branching and crosslinking. The products depend upon several factors such as the relative concentration of phenylethynyl groups, molecular mobility of the growing polymer and conformational restrictions and have been postulated to be predominantly highly conjugated polyenes. In general, the cured resins have a favourable combination of properties including good thermal stability, solvent and moisture resistance and good toughness. The amide acid oligomer solutions were processed into thin films, adhesive tape and carbon fibre prepreg. Neat resin plaques were fabricated from imide oligomer powder by compression moulding. The maximum processing pressure was 1.4 MPa and the cure temperature varied from 350–371°C for 1 h for the composites, adhesive panels and neat resin mouldings. The properties of the cured imide oligomers containing pendent and terminal phenylethynyl groups are compared with those of cured oligomers of similar composition and molecular weight which contain either terminal or pendent phenylethynyl groups. Published by Elsevier Science Ltd.