Iso-concentration ordering kinetics of block copolymers in solution during solvent extraction using dynamic oscillatory measurements

Abstract

The iso-concentration ordering kinetics of poly(styrene-b-butadiene) in a neutral solvent, toluene, at several concentrations along the solvent extraction path at room temperature were studied using dynamic mechanical rheological measurements and SAXS. These experiments are in contrast to more common studies of the ordering kinetics of block copolymers in which phase separation following temperature quenches is considered. Poly(styrene-b-butadiene) in toluene was found to order into hexagonally-packed cylinders beginning at a polymer concentration of 30 wt%. The half-time was found to be governed by a competition between thermodynamic and kinetic effects as concentration changes. An Avrami exponent of 1.0 was obtained at all concentrations and was correlated to two-dimensional diffusion-controlled growth or heterogeneous nucleation and linear growth at higher concentrations. A comparison of the rheological and SAXS data suggested that changes in the dynamic mechanical response during ordering were induced by the development of individual microstructures acting as physical crosslinks. A correlation between microstructure and the Avrami exponent was not found.