Reversible morphological transitions of polystyrene-b-polyisoprene micelles*

Morphological transitions of polymer micelles have long been sought after. Until now, the only way to change morphology was through the addition of a co-solvent or homopolymer. We have demonstrated for the first time that reversible morphological transitions can be caused solely through changes in temperature. Two polystyrene-b-polyisoprene samples with the same sized PS block of 20kDa were purposefully synthesized with PI blocks of 4 and 6kDa to be near the spherical-cylindrical and cylindrical-vesicle boundaries. It was found that only small changes in temperature are needed to cause the morphological change. The cylindrical sample adopted a spherical morphology after heating from 25-35\r{ }C and the vesicle sample became cylindrical upon heating from 25-40\r{ }C. While cylindrical and vesicle micelles were once again observed after cooling the samples back to 25\r{ }C, the fraction and size of the micelles were still increasing after several weeks.