Complex microphase separation and microdomain structures in polyisoprene-block-poly(D₈-styrene)-block-poly(vinyl methyl ether) triblock terpolymer

Microphase separation of a polyisoprene-block-poly(D₈-styrene)-block-poly(vinyl methyl ether) triblock terpolymer were investigated by small-angle neutron scattering and small-angle X-ray scattering. At low temperature, poly(D₈-styrene) (DPS) and poly(vinyl methyl ether) (PVME) are miscible but polyisoprene (PI) is immiscible with both DPS and PVME so that the terpolymer is separated into two microphases, i.e., the PI phase and the phase of DPS and PVME which are moleculary mixed. In the temperature range covered in this experiment, the segregation power between PI and DPS decreases with increasing temperature but that between DPS and PVME increases, while PVME remains immiscible with PI. The competing short-range interactions with the opposite temperature dependences result in a complex but novel MS behavior and a change of the microdomain-structure with temperature as discussed in the text.