Comicellization of binary mixtures of block copolymers with different block lengths in a selective solvent

Comicellizations of poly(a-methylstyrene)-block-poly(p-vinyl alcohol)s (KT-326 and KT-327) with slightly different block lengths in benzyl alcohol are investigated by means of static and dynamic light scattering. The critical micellization temperature (T-1) of KT-326 is lower than that (T-2) of KT-327. The apparent molecular weight, radius of gyration and hydrodynamic radius have been measured for micellar solutions with different KT-326/KT-327 compositions after single-step and double-step temperature jumps (T-jumps) from the unimer region. The following conclusions were deduced. In a single-step T-jump from unimer region I (T > T-2) to region III (T < T-1), where both copolymers form micelles in their respective pure solutions, comicellization takes place to form micelles having a copolymer composition close to the composition of the solution. In a jump from region I to region II (T-1 < T < T-2), where only KT-327 can form micelles in its pure solution, some fraction of KT-326 is incorporated with KT-327 to form comicelles, but the extent of the incorporation is limited even in a solution with a high KT-326 content. In a double-step T-jump from region I to region II, and subsequently to region III after the second jump, some fraction of KT-326 forms comicelles with existing micelles formed in the first jump, while another fraction of KT-326 forms micelles of pure KT-326. Copyright (C) 1996 Elsevier Science Ltd.