Furan-maleimide thermoplast-thermoset merged polyimides

Novel thermoplast–thermoset merged polyimide system has been developed via Diels-Alder intermolecular reaction of bisfuran A namely, 2,5-bis(furan-2-ylmethyl carbamoyl)terephthalic acid with a series of bismaleimides B1–5 containing aliphatic and alicyclic groups in the main chain viz., B1: 1,2–bismaleimido ethane, B2: 2–methyl–1,5–bismaleimido pentane, B3: 1,6–bismaleimido hexane, B4: 2,2,4–trimethyl 1,6–bismaleimido hexane, B5: isophorone bismaleimide. The intermediate Furan—maleimide Diels-Alder adducts C1–5 were aromatized and imidized (i.e. cyclized) through carboxylic and amide groups to afford thermoplast-thermoset merged polyimides D1–5. Synthesized polyimides were characterized by elemental analysis, spectral features, number average molecular weight (\( \overline{\mathrm{Mn}} \)) and thermal analyses. Bulk polymerization was also carried out. Proof of structure was based mainly on a comparison of infrared spectra of polyimides with those of the corresponding model compound 4 prepared from phthalic anhydride and furan–2yl–methanamine in the similar way. FTIR spectral features of polyimides D1–5 were quite identical with the model compound 4. The ‘in situ’ void–free glass fiber reinforced composites GFRC1–5 were prepared and characterized by mechanical, electrical and chemical properties. The ‘in situ’ produced PIs show good adhesion to glass fibers. All the composites showed good mechanical and electrical properties and good resistance to organic solvents and mineral acids.