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AgCl inside porous polymer matrices was obtained by the reaction between the 0.1 M solutions of AgNO3 and NaCl via countercurrent diffusion method. The content of AgCl introduced was determined as a deviation of a polymer weight from the initial one. The amount of precipitated AgCl and the character of accumulation curve versus the countercurrent exposure time depend on a value of the effective volume porosity of a polymer membrane. The rate of the AgCl gain is constant at the early stages of precipitation and further gradually decreases due to the formation of a compact layer inside polymer matrices. The dispersity of the AgCl nanocrystallites was shown by X-ray analysis to depend on the nature of a polymer, i.e. on flexibility of pores’ walls, and on the polymer structure. PET is characterised by a more rigid structure than PP, so the dimension of crystallites obtained in PET matrices (18-40 nm) is considerably less than in PP matrices (60-80 nm). The flexibility of the porous structure can be also changed by an increase of a tensile strain of the initial polymer. At the high tensile strain (400%) the polymer matrices are characterised by a highly oriented and more rigid structure. So the dimensions of crystallites are seen to decrease when a tensile strain is increased. However the dispersity of the AgCl crystallites appeared to be independent at the reaction time. So the increase of AgCl content was carried out through the formation of new crystallites (it is the phenomenon of the secondary crystallization). The evolution of the AgCl layer inside polymer membranes was studied by SEM. At the early stages the individual spherical and cubic aggregates of AgCl of 0.2÷0.6 μm were localized at the boundaries of crazes, pores and along fibrils. One may think that craze fibrils serve as nucleating sites for AgCl phase. Further the aggregates were collected in the dense rod-like structures further are growing into continuous layer with a thickness 10÷15 μm in PET and 20-40 mcm in PP.