The phase behavior of polymers in solution is of both fundamental and practical interest. Previous work using coarse-grained molecular simulations suggests that the critical temperature (Tc) of macromolecules in solution can be controlled by monomer sequence.

Here, the researchers from Princeton's IRG-B group experimentally investigated the solution phase behavior of a series of styrene-isoprene copolymers in both styrene- and isoprene-selective solvents. Across the series, the copolymers had similar overall composition and molecular weight, but subtle changes in monomer sequence obtained by systematically placing a short homopolymer block of either polystyrene or polyisoprene at the end or the center of an otherwise random styrene-isoprene copolymer chain. Compared with a fully-random copolymer, sequences that microphase-separate to form star-like or crew-cut micelles produce a lower Tc. Conversely, sequences that do not form micelles exhibit a higher Tc. Through a delicate balance of solvent/polymer compatibility, the team demonstrates the spontaneous and thermoreversible formation of unusually large (aggregation number ~1000), stable crew-cut micelles. Despite the unusual structure, the thermodynamics of formation of these crew-cut micelles are similar to those of star-like block copolymer micelles.

Macromolecules 57, 3, 916–925 (2024) (ASAP Article)
DOI: https://doi.org/10.1021/acs.macromol.3c02111