Linear and Branched Fiber-like Micelles from the Crystallization-Driven Self-Assembly of Heterobimetallic Block Copolymer Polyelectrolyte/Surfactant Complexes

摘要

The solution self-assembly of a heterobimetallic diblock copolymer with a crystallizable poly-(ferrocenyldimethylsilane) (PFS) core-forming block and a corona-forming segment featuring a poly-(cobaltoceniumethylene) (PCE)-based polyelectrolyte/surfactant complex, PFS50-b-[PCE] [AOT](50) (AOT = bis(2-ethylhexyl) sulfosuccinate), has been explored. Fiber-like micelles were formed in selective solvents for the Co-containing block, yielding a corona in which every repeat unit bears a charge. We found that key features of the one-dimensional (1D) morphologies were dependent on both the polarity of the solvent medium and temperature. In the most polar of the explored solvent media (iPrOH), seeded growth from 1D seeds of PFS50-b-P2VP(739 )(P2VP = poly(2-vinylpyridine)) yielded tapered B-A-B triblock comicelles, where the width of the terminal B region derived from PFS-b-[PCE][AOT](n) reduced on moving from the interface with the seed to the micelle termini. In addition, ca. 30% of the micelles featured branching to yield multiple terminal blocks. On reducing the polarity of the solvent medium by the addition of 20% THF, the tapering of the micelles was no longer apparent, and the degree of branching was substantially increased to ca. 100% of the population. With increased amounts of THF (30%), the degree of branching reduced dramatically to ca. 3%. In the least polar medium investigated (1:10 iPrOH/EtOAc), linear triblock comicelles formed in which the terminal blocks were of consistent diameter, with no evidence for tapering or branching. However, significant unsymmetric growth (i.e., a higher degree of growth from one seed terminus compared to the other) was detected. Post self-assembly modification by coronal counterion exchange to alter the chemistry and solubility of the corona was also explored.