Molecular Weight Dependence of Block Copolymer Micelle Fragmentation Kinetics
Early, J.T.; Block, A.; Yager, K.G.; Lodge, T.P. "Molecular Weight Dependence of Block Copolymer Micelle Fragmentation Kinetics" Journal of the American Chemical Society 2021
We investigate the fragmentation kinetics of block copolymer micelles.
The effect of molecular weight (M) on the fragmentation kinetics of micelles formed by 1,2-polybutadiene-block-poly(ethylene oxide) (PB-PEO) copolymers was studied in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. A series of six samples, with total M ranging from 104 to 105 g mol-1 and nearly constant composition (fPEO ~ 0.4), were examined; all six formed spherical micelles with PEO coronas. Nonequilibrium PB-PEO micelles were prepared by direct dissolution, a process that systematically produces nanoparticles with mean aggregation numbers more than twice the equilibrium values. When subjected to high temperature annealing (170 °C), the average micelle radius was found to decrease substantially, as determined by temperature-jump dynamic light scattering (T-jump DLS) and time-resolved small-angle X-ray scattering (TR-SAXS). The characteristic fragmentation times (tau) were found to increase strongly with increasing degree of polymerization N, as tau ~ N1.8. This result compares favorably with the prediction of a previously untested model.