Poly(p-oxybenzoyl) (POB) crystals were prepared by reaction-induced crystallization during direct polymerization of p-hydroxybenzoic acid in the presence of boronic anhydrides. Polymerizations were carried out at 300 degrees C in dibenzyltoluene at a concentration of 1% with three kinds of anhydrides of boronic acid such as 3,4,5-trifluorophenylboronic acid (TFB), 4-methoxyphenylboronic acid (MPB) and 4-biphenylboronic acid (BPB). The POB crystals were formed as precipitates in the solution and the morphology was considerably influenced by both the structure of the boronic anhydride and its concentration (C-B). Needle-like crystals were firmed in the presence of TFB anhydride (TFBA) at CBS of 5 and 10 mol % by the spiral growth of lamellae. Spherical aggregates of slab-like crystals were formed at CBS from 50 to 100 mol %. The polymerization with MPB anhydride and BPB anhydride (BPBA) also yielded the needle-like crystals at CBS of 50 and 5 mol %, respectively. The polymerization with TFBA at lower C-B was favorable to prepare the needle-like crystal. Molecular weight was also influenced by the structure of the boronic anhydride and C-B. M-n increased generally with C-B and BPBA gave the highest M-n of 14.7 x 10(3) at C-B of 100 mol %. The loose packing of the molecules in the crystal caused by the bulkiness of the end-groups made the polymerization in the crystals more efficiently. Morphology and molecular weight of the POB crystals could be controlled by the chemical structure and the content of boronic anhydride. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1088-1096, 2011