runway polymerization and loss of control of the polymerization process in order to better control the molecular weight distribution of the polyacrylonitrile in the process of polymerization between the suspension comprising animal hair micro powder and the acrylonitrile monomer or between the suspension comprising animal hair micro powder the acrylonitrile monomer and the second monomer or the third monomer or between the suspension comprising animal hair micro powder the acrylonitrile monomer the second monomer and the third monomer a certain amount of chain transfer agents can be added the chain transfer agent is selected from dodecyl mercaptan n octyl mercaptan u03b2 mercaptoethanol and isopropanol the weight percent of the chain transfer agents in all the components of the fiber is 0 1 0 6 particularly 0 1 0 5 and more particularly 0 2 0 4 experiments have shown when the weight percent of the chain transfer agents is less than 0 2 it is difficult to control the molecular weight distribution of the acrylonitrile copolymer when the weight percent of the chain transfer agents is more than 0 4 on the one hand a lot of materials are wasted on the other hand the molecular weight of polymer will be decreased and further the properties of the polyacrylonitrile will be degraded actually in the formula the content of the chain transfer agents is very low in some cases when the agents are added the weight percent of the acrylonitrile monomer and or the second monomer and or the third monomer and or animal hair micro powder may be decreased optionally so that the total weight percent of all components is 100 the animal hair refers to not only animal hair but also animal hair waste or villi.