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)-<i>block</i>-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-<i>b</i>-P2VP^Q) were subjected to the same self-assembly protocol, very different structures were obtained. For PFS₃₆-<i>b</i>-P2VP₅₀₂^Q, the presence of positive charges led to the formation of much shorter rod-like micelles. In contrast, for PFS₁₇-<i>b</i>-P2VP₁₇₀^Q and PFS₃₀-<i>b</i>-P2VP₃₀₀^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

Organometallic–Polypeptide Diblock Copolymers: Synthesis by Diels–Alder Coupling and Crystallization-Driven Self-Assembly to Uniform Truncated Elliptical Lamellae

This paper reports a new synthetic strategy for the preparation of polyferrocenylsilane (PFS) block copolymers (BCPs), by conjugation of two independently prepared homopolymers using Diels–Alder cycloaddition. The PFS blocks were synthesized by photocontrolled ring-opening polymerization, yielding polymers with a cyclopentadienyl end group that serves as a diene in the conjugation reaction. In this initial study we focused on the synthesis of organometallic–polypeptide block copolymers PFS-<i>b</i>-PBLG (PBLG = poly­(γ-benzyl-l-glutamate) using PBLG polymers with a terminal maleimide attached by one-step postpolymerization modification. Five PFS-<i>b</i>-PBLG copolymers with different degrees of polymerization were synthesized and purified by a series of selective precipitations. The self-assembly of these samples was studied in <i><i>N,N</i></i>-dimethylformamide, a solvent selective for PBLG. The BCPs with a PFS block longer than the PBLG block after annealing at 90 °C formed highly uniform platelet micelles with a truncated elliptical shape. Experiments at 75 °C showed that disordered elongated structures formed initially, with fiber-like protrusions from the ends. Over time, the structures became shorter and wider, evolving into uniform truncated elliptical micelles. The process was monitored by X-ray diffraction (XRD) measurements and by ¹H NMR spectroscopy. AFM analysis showed that the micelles were flat and that their thickness increased with the overall chain length of the BCP. Self-assembly of these BCPs in the presence of PFS homopolymer led to formation of flower-like mesostructures consisting of stacks of lamellar petals