Thermally reactive aromatic polyamides

Abstract

Abstract2,5‐Bis(phenylethynyl)terephthaloyl chloride and 4,6‐bis‐(phenylethynyl)isophthaloyl chloride were synthesized in a multistep reaction scheme from 2,5‐dibromoterephthaldehyde and 4,6‐dibromoisophthaldehyde, respectively. Low temperature solution polycondensation of these novel monomers and tolane‐2,4′‐dicarbonyl chloride with aromatic diamines yielded aromatic polyamides containing phenylethynyl moieties. Inherent viscosities of 0.20–0.51 dL/g were recorded. Attempts to carry out the homopolymerization of 2‐(3‐aminophenylethynyl)benzoyl chloride hydrochloride under similar conditions led to low molecular weight polyamide. Under differential scanning calorimetry and thermal mechanical analysis, the polyamides exhibited strong exotherms with onset occurring in the 185–225°C range. The exotherms were attributable to intramolecular cycloaddition of phenylethynyl moieties with amide groups to give polybenzalphthalimidine structures. Curing of a pressed pellet specimen for 16 h at 250°C under a nitrogen atmosphere resulted in partial conversion to a polybenzalphthalimidine structure with a concomitant increase in the polymer glass transition temperature. Isothermal aging in air of the cured specimen at 316°C (600°F) led to 25% weight loss after 200 h.