Abstract
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 ns) 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°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.
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