Incréments d'indice de réfraction de polymères en solution: Étude des lois de mélange. Influence de la masse moléculaire et de la structure

The variation of the refractive index increment (dn/dc) with the molecular weight and the structure of series of linear and branched well-defined polystyrenes dissolved in benzene was studied. Testing the Lorenz-Lorentz and Onsager-Böttcher mixture rules, we were able to show that:

• 1 Below a critical molecular weight of about 2·10⁴, the linear correlation dn/dc=f(1/M_n) is well explained by the influence of chemical heterogeneities included in the polymer chain (end-groups, branching points etc.).
• 2 These rules do not account for specific polymer-solvent interactions and are not quite rigorous.
• 3 The variations of (dn/dc) and the partial specific volume of the polymer, v?_p, observed already for molecular weights higher than 2·10⁴ are accompagnied by a change in the partial specific refractivity. These effects are related to the influence of intramolecular segment density in the interior of the linear or branched coil.

A homologous series of polyoxyethylene-glycols (α-hydro-ω-hydroxypoly(oxyethylene)s) in benzene presents the same behaviour.