The dual self-assembling polycondensation of p-acetoxybenzoic acid (ABA) and p-acetamidobenzoic acid in Therm S 800 was examined at 300 degreesC. Needle-like crystals and lath-like crystals were formed simultaneously through reaction-induced crystallization of oligomers at a molar ratio of 30-50 mol-% ABA in the feed. The needle-like crystals comprised more p-oxybenzoyl units, whereas the lath-like ones contained higher amounts of p-benzamide moieties.