In this paper, deformation and breakup under simple shear of single molten polymer drops in a polymer matrix were investigated. Flow visualization was carried out in a Couette-Flow apparatus under relatively high shear rates and temperatures up to 230 degrees C. Drop/Matrix combinations were composed of polystyrene drops of 0.5-0.6 mm in diameter in polyethylene matrix, and ethylene-propylene copolymer drops of approximately the same size in polypropylene matrix. The deformation and breakup processes were studied under steady state and time-dependent shearing conditions. Either for steady state or time-dependant shearing conditions, drop elasticity generated at relatively high shear rates helped the drops to align perpendicular to the flow direction, i.e., parallel to vorticity axis. Also, the most striking non-Newtonian effects for the high viscosity ratio systems were the Surface erosion and the drop splitting mechanisms. The particles eroded off the main droplet surface were very fine, in the range of 10-50 mu m, and led to a significant reduction in main drop size before its final breakup. (c) 2006 Wiley Periodicals, Inc.