The novel method titled as "mechanotropic spinning" for preparing chemical fibers from polymer solutions is developed. It consists in strong and fast stretching of solution jet, that results in macrolecular orientation, change of Flory-Haggins interaction parameter, phase separation and evaluation of solvent on jet/fiber surface. Theoretical estimation shows that at mechanotropic spinning only 0.1% of solvent remains in solid fiber. This process does not require spinneret and can be realized by jet extension from the dope surface. Evolution of composition and structure of polymer system under spinning as well as rheological properties was studied in details. In addition, the visualization of jet/fiber transformation was done. The main explanation of such components separation process at strong strain of solution is based on induced by mechanical field transition from the viscous to the rubber-like state and pulling out the solvent from solidified jet. This situation was realized for the strong shear deformation as well. The experimental and theoretical results were obtained for solution of copolymers based on acrylonitrile in dimethylsulfoxide.