Soluble, rigid-rod precursor polyimides were prepared via Pd-catalyzed copolycondensation of 3,6-diphenoxy-NJV'-bis(4-bromo-2,5-didodecylphenyl)pyromeUitic diimide, 3,6-diphenyl-NJV,-bis(4-bromo-2,5-didodecylphenyl)pyromellitic diimide, and 2,5-didodecylbenzene-l,4-diboronic acid. From these precursors, soluble, dye-containing polyimides were obtained by nucleophilic substitution of the phenoxy side groups for (a) 4-hydroxyazobenzene, (b) 4,-nitro-4-hydroxyazobenzene, (c) 4-[(4-nitrophenyl)azo]-l-naphthol ("magneson II"), and (d) 2,3'-dimethyl-4-[(2-hydroxy-l-naphthyl)azo]azobenzene ("sudan red B"), respectively.An almost quantitative exchange was achieved in the case of the sterically less demanding dyes (a and b); a low conversion was observed for the bulky dyes (c and d). Throughout, no evidence for chain degradation or other side reactions during the substitution reaction was found by analyzing the products by high-field NMR spectroscopy and membrane osmometry.
A new synthetic approach to soluble, rigid-rod, aromatic polyimides is described. The polycondensation is done by a Pd-catalyzed aryl-aryl coupling of N,N-bis(4-bromo-2,5-didodecylphenyl)-l,2 : 4,5-pyromellitic diimide (2) and 2,5-didodecyl-l,4-benzenediboronic acid (3). Here, the imide structure is already preformed in monomer 2. A structurally identical polymer is synthesized by the classical procedure condensing 1,2 : 4,5-pyromellitic dianhydride (PMDA) (4) and 4,4"-diamino-2,5,2',5',2",5"-hexadode~l-~-terphenyl(5). Both polymers are characterized in detail by 'H and I3C NMR spectroscopy, membrane osmometry and size exclusion chromatography. The average degree of polycondensation is of the order of 15. The thermal behaviour of the polymers is studied by differential scanning calorimetry and thermogravimetrical analysis.
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