TEMPERATURE-CONCENTRATION DIAGRAM OF POLYSTYRENE-BLOCK-POLYDIMETHYLSILOXANE ASSOCIATES FORMED IN DILUTE-SOLUTION OF SELECTIVE SOLVENT

Association behaviour of polystyrene-block-polydimethylsiloxane (PS-bl ock-PDMS) in dilute solution of selective solvent is investigated by s tatic and dynamic light-scattering as a function of temperature and co ncentration. Number-average molecular weights of PS and PDMS blocks ar e 7.8 x 10(3) g mol(-1) and 3.2 x 10(3) g mol(-1), respectively, and t he solvent is a mixture of n-octane (C8) and methylcyclohexane (MCH) w ith the compositions of C8/MCH = 1.23 by weight, which is selective fo r PDMS. On heating the solutions from 12 degrees C to 72 degrees C, th ree different micellar regions are observed over a concentration range of 10(-4)-10(-2) g (g of solution)(-1). The highest temperature regio n right below the unimer region is the so-called anomalous-micellizati on region, where large spherical particles are formed and prow, and ev entually precipitate in a few days. In the second region at intermedia te temperatures, hollow spherical micelles (vesicles) are formed with large association numbers of about 10(3). The third region is located at low temperatures and low polymer concentrations, where hollow cylin drical micelles with the estimated length/diameter ratio of less than 16 are formed. These hollow cylindrical micelles are observed on heati ng only, but not on cooling from the unimer region, so they are presum ed not to be in equilibrium state but to be meta-stable micelles forme d on micellization processes. (C) 1997 Elsevier Science Ltd.