SELF-ASSEMBLY IN MIXTURES OF POLY(VINYL METHYL-ETHER) AND POLYSTYRENE-BLOCK-POLYISOPRENE - 1 - FORMATION OF NANOCOLLOIDAL SPHERES

We studied phase behavior and molecular assembly in blends of poly(vin yl methyl ether) (PVME) and polystyrene-bloch-polyisoprene (SI) by sma ll-angle X-ray scattering (SAXS), transmission electron microscopy (TE M), and light scattering. The neat block copolymer forms bcc (body cen tered cubic) spheres composed of polyisoprene block chains in a matrix of polystyrene block chains. On casting from a toluene solution, the blends with volume fractions of PVME less than or equal to 0.3 experie nced only microphase separation, resulting in a structure with spheric al microdomains of polyisoprene block chains (PI) in a matrix of polys tyrene block (PS) chains (PS-corona) mixed with PVME, while the blends with volume fractions of PVME greater than 0.3 underwent macrophase s eparation into a PVME-rich region and an SI-rich region which was also microphase-separated. Furthermore, a thermoreversible one- to-two-pha se transition induced by the change of segmental interactions between PS-corona and PVME was observed for the cast films. This system can be considered as a two-component system composed of nanocolloidal sphere s of PI with PS-corona and PVME with a LCST phase diagram. The cloud p oint of the nanocolloidal spheres/PVME system is significantly lowered compared to that of a homopolystyrene/PVME blend due to the confineme nt of PS block chains onto the PI spheres. Note that the structures ob served for this system are similar to those observed in colloidal disp ersions of ionic latex particles in water and oil-in-water or water-in -oil microemulsions.