Dual-curing propargyl-phthalonitrile imide-based thermoset: Synthesis, characterization and curing behavior

Oligoimide containing propargyl and phthalonitrile groups in one molecule (OI-PR-PN) was synthesized by a facile and eco-friendly method in benzoic acid melt. To incorporate side propargyl groups into the polyimide backbone, a new monomer was developed – 5-(2-propyn-1-yloxy) benzene-1,3-diamine (PBD). The OI-PR-PN dual-curing behavior was studied by DSC and FT-IR methods. The curing of phthalonitrile groups can be promoted by the intermediates formed during the propargyl groups polymerization. This allows cross-linking of phthalonitrile groups at 300–350 °C in one component system. OI-PR-PN showed good solubility in low boiling point solvents and had low melt viscosity (up to 8 Pa‧s at 250 °C). The temperatures of 10% weight loss of the cross-linked OI-PR-PN and oligoimide containing only propargyl groups (OI-PR) are 496 °C and 450 °C correspondingly. The completely cured OI-PR-PN glass transition temperature measured by dynamic mechanical analysis was 424 °C with a storage modulus 4.2 GPa at 50 °C. The possibility of cross-linking without using curing additives with a combination of excellent thermal and mechanical properties indicates the potential of OI-PR-PN as a matrix for composite manufacturing.