AbstractPolycondensation of terephthalic aldehyde with 2,4 — or 2,6‐dimethyl ‐, or 2,4,6 — trimethylpyridine leads to a new kind of heat‐resistant resin with aromatic‐heterocyclic structure.These resins are mixtures of thermosetting oligomers. A few components have been identified after separation by size‐exclusion chromatography. Although infrared spectroscopy sheds some light on certain aspects of their heat‐curing mechanism, this has not yet been fully elucidated.Derivatives of trimethylpyridine (symmetrical collidine) appear to be particularly interesting in view of their possible use with reinforcing fibre materials for prepreg fabrication. These derivatives lead to composite materials whose high mechanical properties remain unaffected for several thousand hours at 250°C and a few hours at 350°C.These products are being developed on an industrial scale under the n