The phase separation behavior of polymer blends modified by copolymer additives has been studied using light scattering techniques. Block and random copolymers with equal styrene and butadiene content as well as a random copolymer with unequal monomer composition were used as additives at a concentration of 2.5% (w/w). The symmetric additives lowered the phase boundary with increasing concentration while the asymmetric additive destabilized the phase boundary. The data demonstrate a slowing of the kinetics with the addition of any of the copolymers. In comparison to the binary blend, droplet sizes in the early stage were smaller with added symmetric block copolymer and larger with added asymmetric random copolymer. Scaling analysis of the intermediate stage kinetics showed some deviations relative to binary scaling results. Deviations from Porod's law indicate that modifications to the interfacial boundary are most notable for the asymmetric random copolymer. Self-similarity was seen to hold for all of the systems.

Small-angle neutron scattering (SANS) has been employed to study a blend of polystyrene and polybutadiene modified by copolymer additives. SANS data from the one-phase region approaching the phase boundary has been acquired for blends modified by random and diblock copolymers that have equal amounts of styrene and butadiene monomers as well as a random copolymer with an unequal monomer composition. The binary blend is near the critical composition, and the copolymer concentrations are low at 2.5% (w/w). The data have been fitted with the random-phase approximation model (binary and multicomponent versions) to obtain Flory-Huggins interaction parameters () for the various monomer interactions. These results are considered in the context of previous light scattering data for the same blend systems. The SANS cloud points are in good agreement with previous results from light scattering. The shifts in the phase boundary are due to the effects of the additives on the parameter at the spinodal. All the additives appear to lower the parameter between the homopolymers; this is in conflict with the predicted Flory-Huggins behavior.