COMPLEX PHASE-BEHAVIOR OF A DISORDERED RANDOM DIBLOCK COPOLYMER IN THE PRESENCE OF A PARENT HOMOPOLYMER

Previous efforts addressing binary blends of a block copolymer and a p arent homopolymer have principally employed ordered copolymers in eith er the intermediate- or strong-segregation regimes. In this work, blen ds composed of a disordered (75/25)-b-(50/50) ly[(styrene-r-isoprene)' -b-(styrene-r-isoprene)''] (S/I)'-b-(SII)'' random diblock copolymer ( RBC) and homopolystyrene (hS) have been investigated. Blend morphologi es, characterized by transmission electron microscopy are correlated w ith hS concentration and molecular weight, as well as with changes in the hS T-g, as measured by thermal calorimetry. At low hS fractions (u p to 20 wt % hS), the S/I block sequences in the RBC induce competitio n between attractive and repulsive interactions with hS molecules, res ulting in the formation of thin hS channel structures in a continuous RBC matrix. An increase in hS concentration or molecular weight serves to broaden the channels until the morphology resembles macrophase-sep arated hS domains containing micelle-like RBC dispersions. In blends w ith relatively high hS fractions (greater than 80 wt % hS), repulsive interactions between RBC and hS molecules are responsible for the form ation of macroscopic RBC domains in a continuous hS matrix. These blen d morphologies demonstrate that localized interactions between homopol ymer molecules and each block of a copolymer exist, and can be probed, in the disordered state.