Highly thermostable rigid-rod networks constructed from an unsymmetrical bisphthalonitrile bearing phthalazinone moieties

Phthalazinone rigid-rod networks with excellent thermostability have been prepared by the polyaddition of an unsymmetrical phthalonitrile-functional phthalazinone, namely 4-(4-(4-(3,4-dicyanophenoxy)phenyl)-1-oxophthalazin-2(1H)-yl)phthalonitrile (5) in the presence of promoting agents. 5 was readily prepared via nucleophilic displacement of 4-(4-hydroxylphenyl)(2H)-phthalazin-1-one (1) with 4-nitrophthalonitrile (3) under mild conditions. The substitution of N–H in phthalazinone was accomplished via a novel N–C coupling reaction in an essentially quantitative yield, confirmed by spectroscopic studies as well as a model reaction of 4-(4-tolyl)(2H)-phthalazin-1-one (2). Green prepolymers (7a–7c) were obtained by the polymerization of 5 in its melt phase with the charge of aromatic diamines (6a–6c), and with concurrent cyclization a mixture of poly(iminoisoindolenine) oligomers was produced. The obtained amorphous 7a–7c show Tgs ranging from 180 to 190 °C depending on the amine nature. Both 5 and 7a–7c have a non-coplanar conformation and exhibit sufficiently good solubility in common solvents (e.g., DMSO, DMF, DMAc, NMP, CHCl3, etc.), and hence can be processed either from their melt or from solution. The insoluble networks (8a–8c) prepared by direct curing of 5 or by post-curing of 7a–7c exhibit excellent thermal properties together with superior long-term thermo-oxidative stabilities.