Micellisation de copolymères séquencés polystyrène‐polyvinylpyridinium, 3. Influence de la concentration en sel et de la température

The effects of the salt concentration and temperature on the micellization phenomenon of polystyrene‐poly(4‐vinyl‐N‐ethylpyridinium bromide) block copolymers in dilute solution are investigated in solvents selective for the polyelectrolytic part (water‐methanol‐LiBr mixtures). The polystyrene moiety being in non‐solvent media remains rather collapsed whatever temperature and salt concentration. On the contrary, the latter parameters modify strongly the conformation of the soluble polyelectrolytic chains and therefore determine the “quality” of the solvent essentially towards the polyvinylpyridinium blocks. Consequently an increase of the temperature or a decrease of the salt concentration have the same effect on the behaviour of the copolymers. In the case of a copolymer with a small molecular weight polystyrene block (Mw = 2 700), the unimer‐multimer (single molecules/micelles) equilibrium is easily shifted in favour of the single molecules by increasing the temperature or decreasing the ionic strength. On the contrary, if the polystyrene moiety is longer (Mw = 6 000 – 13 000) the micellar weight of the system is little or even not at all influenced by the ionic strength and the temperature. These results emphasize that, for the investigated systems, it is the “insoluble” blocks which essentially govern the micellization phenomenon.