From a theoretical background similar to that of Ghedgaonkar’s

using a general description of breakup and the Smoluchowski theory of coalescence of droplets

a relation has been derived for estimating the dispersed phase droplet size during mixing of polymer blends in the steady state．The influences of dispersed phase concentration

shear rate and elasticity of polymers are studied．In a less concentrated system

the diameter of the droplets increases linearly with their concentration．In a more concentrated system

the coalescence effects become increasingly important

the simultaneous collisions of three and more droplets should be considered and the drop diameter versus concentration dependence becomes more complicated．In PS(dispersed)／PP(matrix) blend system

it was observed that the drop diameter continued to decrease up to a maximum shear rate of 128 S-1．In PS(matrix)／PP (dispersed) blend system

however

as the shear rate increased

the drop diameter initially decreased．At a critical shear rate

the diameter reached a minimum value

and beyond it

the diameter increased with shear．The elasticity ofpolymers plays a crucial role．