Abstract: An acrylic fiber precursor for high performance carbon fibers free of defects which comprises an acrylonitrile polymer containing at least 90% by weight of acrylonitrile and has a surface roughness of 2.0 to 3.0 with dense inner structure. from a solution comprising 24 to 27.5% of the acrylonitrile polymer is dry-jet wet spun into a coagulation bath consisting essentially of dimethylformamide or dimethylacetamide and having a bath temperature of 5.degree. to 25.degree. C.Carbon fibers obtained by carbonizing these precursor acrylic fibers have no fusion bonding or agglutination of filaments and exhibit high performance.

Abstract: A process for producing acrylonitrile-based copolymers for carbon fibers is described, which comprises producing substantially metal-free acrylonitrile-based copolymers containing as essential components at least 95% by weight of acrylonitrile and from 0.5 to 3% by weight of a carboxyl group-containing polymerizable unsaturated monomer, at least 20% of the carboxyl groups being substituted with ammonium ions, in the presence of a redox polymerization initiator comprising ammonium persulfate and ammonium sulfite and, thereafter, spinning the acrylonitrile-based copolymer. The present invention permits production of acrylonitrile-based copolymers free of metal impurities responsible for the formation of defects in the ultimate carbon fibers. High performance carbon fibers can be produced without the need of any additional steps.