The objective of this work is to study the kinetics of changes in the structure and properties of interpolymer complexes obtained on the basis of sodium carboxymethylcellulose polysaccharide (Na-CMC) with urea-formaldehyde oligomers (UFO). The stability period of solutions of Na-CMC interpolymer complexes with UFO determination of viscosity at various temperatures has been studied. Experimental data show that when storing aqueous solutions of Na-CMC, the viscosity decreases due to changes in the structure due to the rupture of polyester bonds, which leads to a decrease in the molecular weight of Na-CMC. With the addition of a urea-formaldehyde oligomer and the formation of a polycomplex, the stability time of the Na-CMC solution increases due to inhibition of the destruction of sodium carboxymethyl cellulose in aqueous systems. The results of the viscosity study are also confirmed by IR spectroscopic data, which show a decrease in the intensity of the absorption band related to the oxygen bridge of sodium carboxymethylcellulose, which leads to a decrease in the viscosity of Na-CMC solutions. Addition of a urea-formaldehyde oligomer to Na-CMC, i.e. the formation of a polycomplex between the constituent components of Na-CMC and UFO leads to an increase in the stability period of Na-CMC solutions by 4-5 times. For stable storage of Na-CMC solutions, solutions of urea-formaldehyde oligomers that inhibit the destruction of the Na-CMC solution can be used as a highly effective preservative.