Surface segregation and bulk thermodynamics in blends of regularly-long branched and linear chains

In this work, the effect of chain architecture on surface segregation and bulk thermodynamics of blends of well-defined star-branched and linear polymers has been studied experimentally for polybutadienes (PB) prepared by anionic polymerization. Bulk thermodynamics were studied sensitively with Small Angle Neutron Scattering. The thermodynamic interaction parameter, χ _eff, was found to vary non-monotonically with an increase in the number of arms, decrease with an increase in star concentration and vary with the molecular weight of each component. The contribution to the bulk interaction parameter due to architectural effects was smaller than that due to the isotopic labeling. PB blends, in which both components were stars, were also studied to determine if the value of χ_eff was the same as that for an isotopic linear/linear blend. Since the non-monotonic increase in χ _eff with the number of arms for the PB blends was the opposite of the previous result for the polystyrene (PS) blends, a third star/linear blend was studied which was poly(methyl methacrylate).; Surface segregation in the PB blends with varying compositions, number of arms of the star, and molecular weight of the linear PB, was studied with Neutron Reflectometry, and Nuclear Reaction analysis. The kinetics of surface segregation in these blends was also probed. Though changes in architecture of one component did affect the degree of surface segregation, the architectural effect was small compared to the labeling effect. One star/star blend was also studied by NR.; Two other effects, the effect of core structure of the star and comb branching, were also studied. Bulk thermodynamics and surface segregation of polystyrene stars with different core structures from that of previous work with PS blends were studied. Core structure appeared to play a role. When the type of branching was changed from star-branching to comb-branching, while the number of arms was kept constant, both the bulk interaction and surface segregation of the PS blend were affected.