THE EFFECT OF SHEAR-FLOW ON THE PHASE-BEHAVIOR OF POLYBUTADIENE POLYISOPRENE BLENDS/

The parameters which control the miscibility of blends of amorphous po lybutadiene and polyisoprene were investigated under equilibrium and f low conditions, using a combined rheometer and light scattering techni ques. Quiescent light scattering cloud point measurements show that th e blends are miscible at room temperature with the miscibility increas ing with the vinyl content of polybutadiene. Temperature jump experime nts were performed by heating the blend from a one-phase to two-phase region, followed by shearing while simultaneously monitoring the devel opment of the scattering patterns and intensities. The results show dr amatic differences in shear rate and shear strain dependent scattered intensities in two mutually orthogonal directions, parallel to and per pendicular to flow directions. These results are interpreted in the li ght of existing models for flow-induced phase behavior in polymer blen ds, including flow-induced miscibility and suppression of fluctuations by flow. (C) 1996 John Wiley & Sons, Inc.