MICELLIZATION KINETICS OF BLOCK-COPOLYMERS IN SELECTIVE SOLVENT

Micellization kinetics of poly(alpha-methylstyrene)-block-poly(vinylphenethyl alcohol) (P alpha MS-b-PVPA) in selective solvent, benzyl alcohol (BA), was investigated by time-resolved static and dynamic light scattering. Time evolution of apparent molecular weight M(wapp), and radius of gyration R(gapp) were measured for two (P alpha MS-b-PVPA)s (KT-326 and KT-327) of different block compositions in the course of micellization after quenching from the unimer region to the micelle region. The micellization was found to proceed stepwise by fast and slow processes. Observed features of time variation of M(wapp) and R(gapp) led to the following conclusions for the micellization processes. In the fast first process, quick association of unimers resulted in the birth of quasi-equilibrium micelles and an increase of the number of quasiequilibrium micelles dominated over growth of the micelle size, The slow second process of approaching the final equilibrium state primarily proceeded by growth of the micelle size, with accompanying decomposition of the quasi-equilibrium micelles and with a gradual decrease of the micelle number. The time evolution of M(wapp) was approximately described by an exponential equation with two time constants of the first and second processes. The time constant tau(1) of the first process depended on the polymer concentration strongly, whereas the time constant tau(2) of the second process was almost independent of the concentration. In the case of KT-327 with longer core chains of PVPA block, the value of tau(1) ranged from 0.1 to 1 h, and the value of zz was several tens of hours. KT-326 had much longer tau(1) by about 10(3) times than tau(1) of KT-327. Both tau(1) and tau(2) of KT-327 decreased with increasing temperature.