Poly(l-oxotrimethylene), obtained by the perfectly alternating polymerization of ethylene and carbon monoxide, was successfully dissolved in composite metal salt solutions such as zinc chloride and calcium chloride aqueous solutions. Certain poly(I-oxotrimethylene) solutions exhibited a phase-separation point of 0degreesC or greater; the different phase-separation temperatures depended on the metal salt composition ratio, the polymer molecular weight, and the polymer concentration. When a solution with a phase-separation point was used for wet spinning, a coagulation temperature below the phase-separation point resulted in gelation of the filament, which was caused by a temperature jump during the coagulation process; this yielded a coagulated filament with a dense and homogeneous cross-sectional structure. The hot drawing of the coagulated fiber produced a high-performance polyketone fiber with high strength and high elastic modulus [tenacity = 18.5 cN/dtex (2.4 GPa); elongation = 5%; elastic modulus = 450 cN/dtex (59 GPa)]. With a solution that exhibited no phase-separation temperature, coagulation proceeded as the coagulant penetrated from the fiber surface into the filament inside, yielding a coagulated filament with a skin-core structure. The maximum tenacity achieved with this skin-core coagulated filament was as low as 15 cN/dtex (1.9 GPa). (C) 2004 Wiley Periodicals, Inc.