Synthesis and properties of high temperature phthalonitrile polymers based on o, m, p-dihydroxybenzene isomers

Abstract

A series of high-temperature phthalonitrile monomers with o, m, p-dihydroxybenzene isomers, namely, 1,2-bis(3,4-dicyanophenoxy) benzene (o-BDB), 1,3-bis(3,4-dicyanophenoxy) benzene (m-BDB) and 1,4-bis(3,4-dicyanophenoxy) benzene (p-BDB), were synthesized via a facile nucleophilic displacement of a nitro-substituent from 4-nitrophthalonitrile. The structures of the monomers were characterized by FTIR, ¹H NMR and WXRD. Curing behaviors of the monomers with 4,4′-diaminodiphenyl ether were recorded by DSC. The result shows that the processabilities of o-BDB and m-BDB are superior to p-BDB due to lower melting points and broader processing windows. The structures of the cured phthalonitrile polymers were characterized by FTIR and WXRD, and thermal stabilities were evaluated by TGA and all the polymers exhibit excellent thermal and thermal-oxidative stabilities. Dynamic mechanical analysis reveals that the polymers have high storage modulus and high glass-transition temperatures. Consequently, o-BDB and m-BDB polymers show more outstanding processability, thermal stability and mechanical properties than p-BDB polymers, which may be good candidates for high-temperature phthalonitrile polymers.