Synthesis of aromatic polyamides containing anthracene units via a precursor polymer approach

Abstract

The Diels-Alder and retro-Diels-Alder chemistry of anthracene were used to synthesize aromatic polyamides analogous to poly( p-phenylene terephthalamide) (PPTA) via soluble precursor polymers. Novel monomers, which are formally Diels-Alder adducts of diaminoanthracenes with maleic- and fumaric-type dienophiles, have been synthesized. Two routes for their preparation were employed: firstly, reduction of 2,6-diaminoanthraquinone to 2,6-diaminoanthracene followed by Diels-Alder reaction and, secondly, nitration of Diels-Alder adducts of anthracene followed by reduction of the nitro groups. These monomers were used to prepare precursor polymers using low temperature solution polycondensation with terephthaloyl chloride and activated polycondensation with terephthalic acid. Copolymers were also prepared with structures closer to PPTA. The precursor polymers were converted into anthracene-containing aromatic polyamides by thermal retro-Diels-Alder reactions at temperatures of about 220°C. Confirmation that the retro-Diels-Alder reaction had taken place was provided by t.g., i.r. and solid-state 13C n.m.r. spectroscopy.