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Solutions of Polymers

المؤلف:  A. Ravve

المصدر:  Principles of Polymer Chemistry

الجزء والصفحة:  48

2026-01-12

466

Solutions of Polymers

Polymers usually dissolve in two stages. First the materials tend to swell and form gels. The gels then tend to disintegrate into true solutions. Agitation only speeds up the process in the second stage. Chains held together by crosslinks will only swell. Crystallinity or strong hydrogen bonding might also keep some polymeric materials from dissolution and the materials only swell. Some general rules about polymer solubility are: (a) Solubility is favored by chemical and structural similarity between the solvent and the polymer. (b) Solubility of the polymer tends to decrease with an increase in molecular weight. When a polymer dissolves, the free energy of solution, DF is negative, while the entropy change, ∆S is positive, because of increased conformational mobility of the polymer. The magnitude of the enthalpy of solution determines whether DF is positive or negative. The heat of mixing, ∆H_mix for binary systems was suggested to be related to the concentration and energy parameters by the expression [7]:

where V_mix is the total volume of the mixture, the molar volumes of the two components are, V1 and V2, respectively, and Ø 1 and Ø2 are their volume fractions. The energies of vaporization are ∆E1 and ∆E2, while the cohesive densities (energy required to remove a molecule from its nearest neighbor) are ∆E1/V1 and ∆E2/V2.