Effect of Self-Assembly on Phase Separation of Di- and Triblock Copolymers Mixed with Homopolymers in Aqueous Solution

The influence of association of amphiphilic diblock (BA) or triblock (BAB) copolymers on phase separation in binary solutions with linear homopolymer has been investigated. The effect of the homopolymer chemistry was investigated by mixing hydrophobically end-capped poly(ethylene oxide) (PEO) with PEO or dextran homopolymers. Diblock copolymers self-assembled into star-like polymeric micelles, while triblocks formed flower-like polymeric micelles that further associate with increasing polymer concentration through bridging. Phase diagrams,were determined and compared with those of mixtures of dextran with PEO homopolymers. For diblock/dextran mixtures, self-assembling favored phase separation, but much less than expected from the increased molar mass due to self-assembly. For triblock/dextran mixtures, self-assembly favored phase separation much more strongly than for diblock copolymers and was :induced principally by the gain in entropy due to the formation of bridges. Macroscopic phase separation was. also observed when large PEO homopolymers were mixed with either diblock or triblock copolymers, but it occurred at much lower Concentrations in thee latter case. Incompatibility due to different chemistry is more important than different architecture as a driving forte for phase separation for mixtures of homopolymers with diblock copolymers, whereas for mixtures with triblock copolymers the architecture is more important.