Kinetics of chain exchange in body-centered cubic block copolymer nanostructures

The process of chain exchange, whereby an individual block copolymer spontaneously escapes from one micelle and subsequently re-inserts into another, can be followed quantitatively by time-resolved small-angle neutron scattering (TR-SANS). A great deal is now known about the dependence of the escape time on core and corona block lengths, for diblock and triblock micelles in dilute solution. However, performing such measurements at higher concentrations, in the ordered state, is challenging. We will describe recent measurements of exchange in polystyrene-block-poly(ethylene-alt-propylene) (PS-PEP) diblocks in squalane, up to concentrations as high as 50%, where the individual micelles pack onto a BCC lattice. Furthermore, the effect of adding free PEP chains into the intermicellar spaces is also quantified. The results are interpreted in the context of enthalpic and entropic contributions to the escape barrier from both core and corona blocks.