Morphosynthesis of poly[4-(1,4-phenylene)oxyphthalimide] (POPI) and poly[4-(1,4-phenylene)oxyphthalimide-co-4-phthalimide] (POPI-PPI) was examined by using the crystallization during the polymerization. The POPI fibrillar crystals were obtained as precipitates with the formation of spherical aggregates of plate-like crystals. Some of the POPI fibrillar crystals were longer than 15 mu m. They possessed high crystallinity and the molecules aligned perpendicular to the long direction of the fibers. On the other hand, one-dimensional structures of POPI-PPI such as ribbon, cone, rod, and fiber were obtained as precipitates by the copolymerization. The copolymer molecules might align along the long direction of the cone-like crystals. The morphology of these poly(ether-imide)s could be controlled by not only the polymerization condition but also with the aid of copolymerization. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012