The gel relaxation times of two different poly[styrene-b-(ethylene-alt-propylene)-b-styrene] (SEPS) ABA triblock copolymers in squalane at various concentrations has been measured by rheology. These relaxation times were compared with the results of previous time-resolved small-angle neutron scattering (TR-SANS) experiments, which measured chain exchange kinetics in SEP diblock and SEPS triblock micelles in squalane. The gels relaxed up to four orders of magnitude faster than expected based on the chain exchange measurements of equivalent diblock polymers. By accounting for two factors - a bias toward shorter end-block lengths in the gel relaxation, and a reduction in the energy barrier to chain pullout caused by the triblock architecture - a model is constructed that reconciles the surprisingly short gel relaxation times with the chain exchange times measured via TR-SANS.
Bibliographical noteFunding Information:
This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. Data were collected using an instrument funded by the National Science Foundation under Award No. 0960140. We thank Dr. Jie Lu for the SEPS (45?144?45) polymer previously produced.
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