Polymer Solution

a uniform, thermodynamically stable, and molecularly dispersed mixture of polymers and liquids of low molecular weight. The study of the optical, electrical, and hydrodynamic properties of diluted polymer solutions, in which the macromolecules are separated from each other, yields quantitative information on the molecular weight and the molecular-weight distribution of the polymer solute and on the dimensions, shape, and rigidity of the macromolecules.

The increase in the intermolecular interaction with increasing concentration leads to the appearance of a three-dimensional network of bonds in polymer solutions and, eventually, to gel formation and the formation of fluctuant or stable aggregates of various forms that may approach the dimensions of colloid particles. The boundaries separating polymer solutions, gels, and colloid systems are arbitrary, and the determination of such boundaries may depend on the method of study. The solubility of polymers depends on the chemical structure of their chains, the nature of the solvent, and the temperature.

The flexibility of macromolecules leads to independent motion of separate molecular segments in polymer solutions, which is reflected in such properties as the sharp increase in the number of particles of the solute relative to the solvent’s true content. Thus, polymer solutions are characterized by very high viscosity, a strong concentration dependence of the viscosity, and a series of thermodynamic anomalies relative to solutions of compounds of low molecular weight. Owing to the low rate of diffusion of macromolecules, a very slow approach to the equilibrium state is observed upon mixing, and the formation of polymer solutions takes place through the stage of polymer swelling. Polymer solutions have viscoelastic properties, whereas concentrated polymer solutions, similar to rubbers, are capable of high-elastic deformation.

Polymer solutions are used in producing fibers, films, glues, lacquers, paints, and other items made of polymer materials. The introduction into the polymer of small amounts of a solvent (plasticizer) reduces the temperature of glass transition, the yield temperature, and the viscosity of the melt.