Comparison of Gel Relaxation Times and End-Block Pullout Times in ABA Triblock Copolymer Networks

Abstract

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.