AbstractStages of formation in the structure of precipitated polymer phase have been found by the method of spectroturbidimetric titration (STT) during precipitation titration of a number of polymer systems. In the first stages of formation of polymer particles, a sharp decrease was observed in the particle size, rCλ, which may be related to a fall in large fluctuations in the postcritical region if the transition of the system through the binodal curve were to be identified with phase transition of the second kind. In the second stage, rλ remains constant at the minimal level, rλ = rλ(γ) = rλ 0 const. The extension of plateau rλ 0 in terms of γ depends on the polymer‐solvent‐precipitant system(P‐S‐P) and conditions of titration. The value of rλ 0 differs insignificantly for different systems, rλ 0 = 0.2–0.3 μm, which is possibly related to the existence of an optimum of particle size in colloid systems of this type. The third stage is determined by the process of particle coagulation, here the kinetics are subject to the equation of Smolukhowskii and the rate depends on the P‐S‐P system. A value of v was determined which appears to be antibate to the effectiveness of attractive forces produced between polymer particles and defines the coagulation process in a specific P‐S‐P system. General conditions for the preservation of particle size during titration were established. Under these conditions, however, an effective separation of fractions with respect to molecular weights can not be attained from the point of view of relaxation thermodynamics. These contradictions are minimized by the use of the STT method. It is shown that the coagulation of particles during turbidimetric titration by the conventional approach leads either to fallacious underestimation or overestimation of the polymolecularity of a polymer depending on the time of beginning of such coagulation, before or after complete precipitation of the polymer.