Preparation of the poly (p-oxybenzoyl -co-p-mercaptobenzoyl) whiskers was examined by means of the crystallization of oligomers during solution polymerization. Polymerizations were carried out in liquid paraffin at the concentration of 1.0% and 300 degreesC for 6 h. Copolymerization of 4-acetoxybenzoic acid and S-acetyl-4-mercaptobenzoic acid did not yield the whiskers. This was attributed to tendency that the copolymerization reduced the crystallizability of oligomers and induced the liquid-liquid phase separation of oligomers due to the lower freezing point. In order to induce short distance sequence regularity into oligomers, copolymerizations of two among four monomers were conducted, which were 4-(4-acetoxybenzoyl)oxybenzoic acid, S-(4-acetoxybenzoyl)-4-mercaptobenzoic acid, 4-(S-acetyl-4mercaptobenzoyl)oxybenzoic acid and S-(S-acetyl-4-mercaptobenzoyl)-4-mercaptobenzoic acid. The copolymerizations of two of these monomers yielded the whiskers but for that of 4-(4-acetoxybenzoyl)oxybenzoic acid and S-(S-acetyl-4-mercaptobenzoyl)-4-mercaptobenzoic acid. The short distance sequence regularity of oligomers brought about the crystallization of oligomers, leading to the formation of whiskers. (C) 2004 Elsevier Ltd. All rights reserved.