Assembly Behavior of Bottlebrush Random Copolymers at the Water/Toluene Interface*

We investigated the assembly of bottlebrush random copolymers (BRCPs) at the water/toluene interface. BRCPs with poly(dimethylsiloxane) (PDMS, hydrophobic) and poly(ethylene oxide) (PEO, hydrophilic) as the sidechains were synthesized by ring-opening metathesis polymerization using ruthenium benzylidene catalysis. Our experiments showed a strong relationship between the interfacial assembly kinetics and the molecular weight of the polymer. The relaxation behavior was investigated further by fitting the interfacial tension (IFT) vs time plot with two exponential decay functions to extract two characteristic relaxation times. The results showed that the relaxation time for BRCP adsorption to the fluid-fluid interface increased, while the relaxation time associated with reconfiguration of the polymers decreased with increasing molecular weight. We further investigated the time-dependent relaxation behavior and the collective diffusion coefficient by fluorescence recovery after patterned photobleaching (FRAPP). The results provide both fundamental understanding of the interplay between molecular weight and assembly behavior at liquid interfaces, and the generalized design rules for bottlebrush polymers as surfactants.