College of Science & Engineering
When a diblock copolymer (AB) is dissolved in a solvent selective for one of the blocks, the polymers can undergo microscopic phase separation and form micelles. Understanding the kinetics of chain exchange between micelles in these systems is crucial to proper control of such micelles in applications ranging from drug delivery, viscosity modification, and plastics toughening. Recently it was found that a BAB triblock copolymer exchanged three orders of magnitude faster than the equivalent AB diblock copolymer when immersed in a B selective solvent. These researchers use a dissipative particle dynamics (DPD) technique to probe the mechanism for this rapid chain exchange, as well as the dependence of chain exchange on system properties such as χ, χN, end-block length, and asymmetry in the end-block lengths. They compare these results to experimental results obtained via time-resolved small-angle neutron scattering of polystyrene (PS)-block-poly(ethylene-alt-propylene) (PEP) in squalane. They also use the same DPD technique to study the chain exchange and endblock pullout time in ABA triblock copolymers, which were found to exchange more rapidly than expected based on previous diblock chain exchange experiments.