How a Small Modification of the Corona-Forming Block Redirects the Self-Assembly of Crystalline-Coil Block Copolymers in Solution

In this study, we examine how the self-assembly of crystalline-coil block copolymers in solution can be influenced by small changes in the chemical structure of the corona-forming block. Three samples of poly(ferrocenyldimethylsilane)-block-poly(2-vinylpyridine) that form long fiber-like micelles uniform in width in 2-propanol, were treated with methyl iodide to convert a small fraction (0.1% to 6%) of the pyridines to methylpyridinium groups. When these partially quaternized samples (PFS-b-P2VP(Q)) were subjected to the same self-assembly protocol, very different structures were obtained. For PFS36-b-P2VP(502)(Q), the presence of positive charges led to the formation of much shorter rod-like micelles. In contrast, for PFS17-b-P2VP(170)(Q) and PFS30-b-P2VP(300)(Q), complex platelet structures were obtained. We explain the complexity of these structures in terms of a distribution of compositions, in which the polymer chains with the highest extent of methylation are the least soluble in 2-PrOH and the first to associate, leading to two-dimensional aggregates. The less quaternized polymer chains remaining in solution have a stronger tendency to form elongated fiber-like micelles that grow from the ends of the initially formed planar structures. In this way, we show that small extents of chemical modification of the corona forming chains can modify the self-assembly process and that simple one-pot protocols can lead to diverse hierarchical structures.