Effect of Concentration on the Dissolution of One-Dimensional Polymer Crystals:A TEM and NMR Study

We report a study of the dissolution of core-crystalline polyferrocenyl­dimethylsilane-<i>block</i>-polyisoprene (PFS₅₃-<i>b</i>-PI₆₃₇, where the subscripts are the degrees of polymerization of the two blocks) micelle fragments in decane for different concentrations (ranging from 0.01 to 6 mg mL^–1) by a combination of transmission electron microscopy (TEM) and high-temperature ¹H NMR. We used self-seeding experiments at different temperatures as an efficient, although indirect, way to evaluate the dissolution of these micelles fragments. We annealed micelle fragment solutions at five different temperatures (50, 60, 65, 70, and 75 °C) for 30 min and cooled them to room temperature to regrow the micelles. The amount of micelle fragments that dissolved at the annealing temperature was then evaluated by comparing the length of the regrown micelles with that of the starting micelle fragments. We show that seed crystallites are less prone to dissolution as their concentration increases. In addition, by combining results of self-seeding experiments and ¹H NMR measurements at 75 °C, we evaluated the percentage of unimer released upon the partial dissolution of seed fragments at 75 °C and established that the mechanism of seed fragment dissolution is also concentration dependent: at low concentrations, they dissolve in a cooperative process, whereas at high concentrations, they dissolve partially from both ends

Hierarchical Polymer–Carbon Nanotube Hybrid Mesostructures by Crystallization-Driven Self-Assembly

Multistep crystallization-driven self-assembly has great potential to enable the construction of sophisticated hybrid mesostructures. During the assembly procedure, each step modifies the properties of the overall structure. Here, we demonstrate the flexibility and efficiency of this approach by preparing polymer–carbon nanotube (CNT) hybrid mesostructures. We started by growing polyferrocenyldimethylsilane (PFS) homopolymer crystals onto multiwalled CNTs. This first step facilitated the redispersion of the coated CNTs in both polar (2-propanol) and nonpolar (decane) solvents. In the second step of hybrid construction, a unimer solution of a PFS block copolymer was added into the PFS-CNT solution. The PFS coating on the CNT initiated the growth of elongated micelles, resulting in structures that resembled hairy caterpillars. PFS-<i>b</i>-P2VP (P2VP = poly-2-vinylpyridine) micelles were grown from the surface of PFS-CNT hybrids in 2-propanol, and PFS-<i>b</i>-PI (PI = polyisoprene) micelles were grown from these hybrids in decane. These micelles, by transmission electron microscopy were seen to have an unusual wavy kinked structure, very different from the uniform smooth structures normally formed by both block copolymers. For hybrids with PFS-<i>b</i>-PI micelles, cross-linking of the micelle coronas locked the whole structure in place and allowed us to use the partial oxidation of PFS components to grow metal nanoparticles in the core of these micelles. We finally investigated the influence of the corona-forming block used to grow the micelles on the wettability of films made from these mesostructures. Films formed with CNT hybrids grafted with PFS-<i>b</i>-PI micelles were superhydrophobic (contact angle, 152°). In contrast, the surface of the films was much more hydrophilic (contact angle, 54°) when they were prepared from CNT hybrids grafted with PFS<i>-<i>b</i>-</i>P2VP micelles

Lateral Growth of 1D Core-Crystalline Micelles upon Annealing in Solution

The emergence of one-dimensional (1D) micelles obtained from the crystallization driven self-assembly (CDSA) in solution of crystalline-coil block copolymers has opened the door to the fabrication of a variety of sophisticated structures. While the development of these fascinating nanomaterials is blossoming, there is very little fundamental work dedicated to understanding the morphological evolution of these 1D micelles in solution. Here, using a combination of transmission electron microscopy, electron tomography, and static and dynamic light scattering, we studied the effect of annealing on a colloidal suspension of 1D micelle fragments formed by the self-assembly of a crystalline-coil poly­(ferrocenyldimethylsilane)-<i>block</i>-poly­(isoprene) (PFS-<i>b</i>-PI) block copolymer in decane, a solvent selective for PI. We are particularly interested in studying the evolution of the rectangular cross-section of the crystalline core of these micelle fragments. By electron tomography, we observed that the shorter dimension of the cross-section became even thinner upon annealing at elevated temperatures, while the longer dimension increased. In parallel, we observed an increase in packing density of the crystalline block as the fragments were annealed at temperatures above 60 °C. From these results, we concluded that annealing the micelle fragments induces a thinning of the crystalline core coupled with a lateral growth

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