Phthalonitrile-functional multiple arylene ether nitrile-containing phthalazinone moiety: facile synthesis, curing, and properties

This article discloses a series of processable multiple phthalazinone-based ether nitriles with various contents of phthalonitrile ends (compounds 4a-4e) and compares the cyclization feasibility of terminal phthalonitrile and pendant cyano group. Compounds 4a-4e were synthesized by facile polycondensation of excess 4-(4-hydroxyphenyl)-2,3-phthalazine-1-one (compound 1) with 2,6-difluorobenzonitrile (compound 2), followed by end-capping of 4-nitrophthalonitrile (compound 4). Their number-averaged molecular weights (M(n)s) and glass transitions can be well tailored by adjusting reactant ratio. Compounds 4a-4e are readily soluble in N-methyl-2-pyrrolidone, N, N-dimethylacetamide, dimethyl sulfoxide, N, N-dimethylformamide, and chloroform and hence can be processed either from their solutions or from melts. On mixing with trace amount of bis(4-aminophenyl) sulfone (compound 5), all oligomers were cross-linked to insoluble networks (compounds 6a-6d) except the high-molecular-weight 4e with the lowest phthalonitrile content. The phthalonitrile is found to be an effectively reactive site for cross-linking, whereas the pendant cyano group in multiple ether nitriles hardly undergoes any reaction confirmed by model reaction. Compounds 6a-6d maintain good structural integrity upon heating to 450 degrees C and exhibit superior thermal stabilities compared with the known phthalazinone polymers. Compounds 6a-6d exhibit high flexural strength (98-111 MPa) as well as limited water absorption (2.2-2.7 wt%) under ambient conditions over a course of 30 days, permitting them to be promising candidates for organic electronics and automotives.