The study of amphiphilic block copolymers in selective solvents

When an amphiphilic block copolymer is placed in a selective, the polymer associates to form micelles in solution. Static and dynamic light scattering as well as small angle neutron scattering methods has been used to study poly (styrene)-b-poly (isoprene) PS-PI micelles of varying compositions in selective solvents. The critical micelle concentration, aggregation number, radius of gyration, and hydrodynamic size of the block copolymers have been measured and compared to theoretical models. Additionally results show that mixed micelles are formed when two PS-PI diblock copolymers are mixed in solution. In studying these mixtures, we not only provide experimental evidence that support models for formation of mixed micelles, but also gain insight in the behavior of mixtures of diblock copolymers in the limit where the molecular weight of one of the copolymers is much smaller than the other.; When compressed into its liquid or supercritical state carbon dioxide becomes a selective solvent for many block copolymers. Carbon dioxide provides an attractive solvent alternative for a wide variety of chemical and industrial manufacturing processes, because of its low cost, wide availability, and environmentally and chemically benign nature. Many CO₂ applications are enabled by the use of diblock copolymers. The design, synthesis and study of these diblock copolymers in CO₂ is therefore fundamentally important. The self-assembly of PtBMA-b-PFOMA copolymers into micelles in CO₂ has also been demonstrated using scattering methods. Complimentary static and dynamic light scattering measurements have been used to study the fundamental solution properties of the polymers in CO₂. With high-pressure light scattering experiments we have shown that some of these polymers in CO₂ exhibit a critical micelle density (cmd). In addition to measuring a cmd, we have developed extensive surfactant-CO₂ phase diagrams for these systems. With SANS measurements, we have demonstrated that these micelles can stabilize insoluble homopolymer into a CO₂ continuous phase.