Micellisation de copolymères séquencés polystyrène‐polyvinylpyridinium, 1. Méthodes d'études. Influence de la nature du solvant

The dilute solution properties of polystyrene‐poly(4‐vinyl‐N‐ethylpyridinium bromide) block copolymers (PS‐PVPQ) are studied in solvents selectively solvating polyelectrolytic moieties (mixtures: water‐methanol‐0,1 M LiBr). For these multicomponent systems, the validity of the data given by light scattering, viscosity and sedimentation velocity measurements, is discussed. Diblock copolymers exhibit four different types of behaviours, depending on solvent composition. The macromolecules are dissolved singly in methanol, but they are associated when water is present. When the water content increases, the association degree passes through a maximum. Since the solutions may contain two species of particles, i.e. the single molecules and the multimers with a narrow weight distribution, the term of micellization for this association phenomenon is correct. Despite their high “molecular weight”, the micelles are small and hence they are very compact. Unlike results from other micellar polymeric systems, the micelle occurrence is accompanied by an increase of the intrinsic viscosity. The hydrodynamic volume of a micelle does not depend on the micellar weights; this can be explained by a star‐like micellar model. Thus, the parameter determining the size of a micelle is not the number of molecules per micelle, but the length of the “branches”, i.e., the “soluble” blocks.