Static and dynamic properties of block-copolymer solution in poor solvent I. A light scattering study on solutions in weakly-selective solvents

By means of static and dynamic light scattering, we investigate competitive behavior of association and liquid-liquid phase separation in solutions of two diblock copolymers in weakly-selective poor solvent. Near the critical point of liquid-liquid phase separation, the copolymer consisting of chemi cally similar blocks poly(dimethylsiloxane) (PDMS) and poly(1,1,3,3-tetrame thyldisiloxanylethylene) (PTMDSE) shows very weak association, exhibiting t he ordinary critical behavior of 5-dimensional (3D) Ising model, but the co polymer consisting of chemically dissimilar blocks of PDMS and polystyrene (PS) shows two modes in static and dynamic light scattering, showing increa sing association as well as the critical concentration fluctuation with the liquid-liquid phase separation being approached. The static critical behav ior obeys the 3D Ising model as in PDMS-block-PTMDSE, while the copolymer a ssociations bring about unique dynamic properties in poor solvent different from those of homopolymer solutions.