Remarkable Effect of Molecular Architecture on Chain Exchange in Triblock Copolymer Micelles

Abstract

The effect of polymer architecture on molecular exchange in block copolymer micelles has been investigated using time-resolved small-angle neutron scattering (TR-SANS). Narrowly dispersed symmetric PEP−PS−PEP and PS−PEP−PS triblock copolymers were synthesized, where PS and PEP refer to poly(styrene) and poly(ethylene-alt-propylene), respectively. Spherical micelles of the triblocks in squalane, a selective solvent for the PEP blocks, were prepared using a cosolvent method. PEP−PS− PEP forms "hairy" micelles with the PS blocks looped in the cores, while PS−PEP−PS forms "flower-like" micelles with most of the PEP blocks looped in the corona. The micelle structure was characterized by small-angle X-ray scattering, providing in particular the core radius as a function of temperature. TR-SANS experiments were conducted on solutions containing 1 and 6 vol % PEP−PS− PEP, and 0.25 and 0.5 vol % PS−PEP−PEP, using matched pairs of deuterium-labeled (dPS) and normal (hPS) specimens and a mixture of normal and perdeuterated squalane contrast-matched to uniformly mixed hPS/dPS micelle cores. Blends of micelles with initially pure hPS and dPS cores produce scattering intensity that decays with the redistribution of block copolymer chains as a function of time, providing direct access to the rate of molecular exchange. Remarkably, the two triblock architectures display exchange rates that differ by approximately 9 orders of magnitude, even though the solvophobic PS blocks are of comparable size. This discovery is considered in the context of a model that successfully explained the exchange dynamics in PS−PEP diblock copolymer micelles.

Amphiphilic poly(disulfide) micelles and a remarkable impact of the core hydrophobicity on redox responsive disassembly

“…20 Dynamic light scattering (DLS) study (Fig. Thus although having contrasting thermal properties, it appears both the disulfide blocks aggregate in similar fashion 21 (Fig. Thus although having contrasting thermal properties, it appears both the disulfide blocks aggregate in similar fashion 21 (Fig.…”

Full Gamut Wall Tunability from Persistent Micelle Templates via Ex Situ Hydrolysis

“…In contrast, the actual diameter of a micelle is determined by the processing history where changing conditions alter both the equilibrium size and the chain exchange kinetics. For example, single chain exchange was found to have a chain exchange rate that scaled with a double exponential dependence on χN . Here the χ term is largely an enthalpic parameter that corresponds to the energy of the core block forming an interface with the solvent phase.…”

Cavitation-enabled rapid and tunable evolution of high-χN micelles as templates for ordered mesoporous oxides

“…4 In this later example, high molar mass block copolymer micelles generated ∼80 nm macropores in antimony-doped tin oxide electrodes. [21][22][23][24][25] For example, a study by Bates et al found that a high-χN system of poly (ethylene oxide-b-butadiene) in water exhibited negligible chain exchange after 8 days. For example, persistent micelle templating (PMT) uses kinetically trapped micelles for the fabrication of highly tunable porous materials with independent control over both the pore size and the material wall thickness.…”