Polyferrocenylsilane Block Research Articles

Defect-Induced Secondary Crystals Drive Two-Dimensional to Three-Dimensional Morphological Evolution in the Co-Self-Assembly of Polyferrocenylsilane Block Copolymer and Homopolymer.

Bottom-up fabrication protocols for uniform 3D hierarchical structures in solution are rare. We report two different approaches to fabricate uniform 3D spherulites and their precursors using mixtures of poly(ferrocenyldimethylsilane) (PFS) block copolymer (BCP) and PFS homopolymer (HP). Both protocols are designed to promote defects in 2D assemblies that serve as intermediate structures. In a multistep seeded growth protocol, we add the BCP/HP mixture to (1D) rod-like PFS micelles in a selective solvent as first-generation seeds. This leads to 2D platelet structures. If this step is conducted at a high supersaturation, secondary crystals form on the basal surface of these platelets. Co-crystallization and rapid crystallization of BCP/HP promote the formation of defects that act as nucleation sites for secondary crystals, resulting in multilayer platelets. This is the key step. The multilayer platelets serve as second-generation seeds upon subsequent addition of BCP/HP blends and, with increasing supersaturation, lead to the sequential formation of uniform (3D) hedrites, sheaves, and spherulites. Similar structures can also be obtained by a simple one-pot direct self-assembly (heating-cooling-aging) protocol of PFS BCP/HP blends. In this case, for a carefully chosen but narrow temperature range, PFS HPs nucleate formation of uniform structures, and the annealing temperature regulates the supersaturation level. In both protocols, the competitive crystallization kinetics of HP/BCP affects the morphology. Both protocols exhibit broad generality. We believe the morphological transformation from 2D to 3D structures, regulated by defect formation, co-crystallization, and supersaturation levels, could apply to various semicrystalline polymers. Moreover, the 3D structures are sufficiently robust to serve as recoverable carriers for nanoparticle catalysts, exhibiting valuable catalytic activity and opening new possibilities for applications requiring exquisite 3D structures.

Uniform Toroidal Micelles via the Solution Self-Assembly of Block Copolymer–Homopolymer Blends Using a “Frustrated Crystallization” Approach

Toroidal nanostructures are of growing importance due to their unique geometry and potential utility in materials fabrication. Although a variety of amphiphilic block copolymers has been shown to self-assemble into toroidal micelles, the conventional methods used are often very slow with little control over the size of the resulting nanostructures. Here, we report a rapid and efficient synthetic route to prepare toroidal micelles of near uniform diameter through the cooperative coassembly of amorphous blends of polyferrocenylsilane block copolymer and homopolymer, where the degree of polymerization of the core-forming metalloblock in the former is greater than for the latter. The self-assembly process is accomplished within a few minutes, and the ring size of the toroids can be varied between 30 and 90 nm by adjusting the mass ratio of the block copolymer and homopolymer. The kinetic stability of the resulting toroidal micelles can be enhanced by frustrating core crystallization through solvent modulation...

Synthesis, thin-film self-assembly, and pyrolysis of ruthenium-containing polyferrocenylsilane block copolymers

The self-assembly of a ruthenium-containing polyferrocenylsilane in bulk and thin films yielded spherical or cylindrical domains in a PS matrix; pyrolysis provided a route to bimetallic Fe/Ru NPs for potential catalytic applications.

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-b-PBLG (PBLG = poly(γ-benzyl-l-glutamate) using PBLG polymers with a terminal maleimide attached by one-step postpolymerization modification. Five PFS-b-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 N,N-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.

Branched Cylindrical Micelles via Crystallization-Driven Self-Assembly

We report the preparation of branched micelles by the growth of thinner-core cylindrical micelles at the termini of the thicker-core cylindrical micelle seeds through crystallization-driven self-assembly of polyferrocenylsilane block copolymers. The branched micelles possessed structures with monodisperse middle segments and, in most cases, two branches at the seed terminus. After cross-linking of the coronas, the branched micelles become resistant to dissolution in good solvents for both blocks and can be manipulated as colloidally stable nanomaterials.

Multi-Armed Micelles and Block Co-micelles via Crystallization-Driven Self-Assembly with Homopolymer Nanocrystals as Initiators

We report the preparation of multi-armed micelles and block co-micelles using the crystallization-driven self-assembly of crystalline-coil polyferrocenylsilane block copolymers from nanocrystals of the homopolymer. The resulting multi-armed micelles possessed hierarchical multipod structures with monodisperse and tunable arm lengths. The termini of the arms remained active to the addition of further block copolymer unimers, and multi-armed block co-micelles with segmented arm chemistries and variable segment sequences were prepared. Coronal cross-linking followed by nanocrystal dissolution led to the release of non-centrosymmetric AB cylindrical diblock co-micelles.

Modular Synthesis of Polyferrocenylsilane Block Copolymers by Cu-Catalyzed Alkyne/Azide “Click” Reactions

This paper reports a new synthetic strategy for the preparation of polyferrocenylsilane (PFS) block copolymers. The block copolymers were prepared by Cu-catalyzed alkyne/azide cycloaddition of two homopolymer precursors that allows access to new functional PFS block copolymers (e.g., polyferrocenylsilane-block-poly(N-isopropylacrylamide)) (PFS-b-PNIPAM)). Trimethylsilyl-protected, alkyne-terminated PFS homopolymer was first prepared via living anionic polymerization, terminating living PFS with commercially available 4-[(trimethylsilyl)ethynyl]benzaldehyde. Subsequent deprotection of the trimethylsilyl group with NaOMe yielded the ethynyl-terminated PFS (ω-alkyne-PFS). This method should be readily applicable to other polymers prepared by living anionic polymerization. Subsequently, non-PFS homopolymers containing a complementary “clickable” azide functional group were synthesized either by anionic polymerization, modification of a commercially available polymer, or atom transfer radical polymerization vi...

Hierarchical Organometallic Materials: Self-Assembly of Organic–Organometallic Polyferrocenylsilane Block Polyelectrolyte–Surfactant Complexes in Bulk and in Thin Films

The self-assembly of well-defined organic–organometallic polystyrene-b-poly(ferrocenylmethyl(dimethylaminopropynylsilane)) (PS-b-PFAMS) diblock copolymers has been systematically investigated by varying the volume fraction of the organometallic block (PFAMS). Quaternization of the PFAMS block yielded PS-b-qPFAMS, which was ionically complexed to the anionic surfactants sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and sodium bis(2,2,3,3,4,4,5,5,5-nonafluoropentyl) sulfosuccinate (AOTF). The self-assembly of the block copolymer-surfactant complexes was also studied in bulk and thin films and produced materials with structural hierarchy over multiple length scales as shown by AFM, TEM, and SAXS studies.

Synthesis, Self‐Assembly, and Applications of Polyferrocenylsilane Block Copolymers

The incorporation of metal atoms into synthetic polymer chains leads to desirable properties and generates a new and versatile class of functional materials with enhanced processability. New creative approaches have led to macromolecular structures in which metals are not only incorporated via the use of traditional covalent bonds but also by potentially reversible coordination interactions. Metallopolymers with precisely controlled chain length are therefore attracting rapidly expanding attention as a result of their properties and potential applications. This article focuses on polyferrocenylsilanes and polyferrocenylsilane block copolymers where iron and silicon are present in the main chain of the organometallic segment. These materials also represent an area of rapidly growing interest as a result of their self‐assembly. The resulting nanostructured materials have a wealth of potential applications and recent breakthroughs in this area are discussed. The subject matter of the article is divided up into subsections covering polyferrocenylsilane homopolymer and block copolymer synthesis, solution and solid state self‐assembly, and applications.

Density control of single-walled carbon nanotubes using patterned iron nanoparticle catalysts derived from phase-separated thin films of a polyferrocene block copolymerElectronic supplementary information (ESI) available: synthesis of PS-b-PFEMS, SWNT growth and characterization. See http://www.rsc.org/suppdata/jm/b4/b403831b/

Single-walled carbon nanotube (SWNT) density and bundle size has been controlled by a simple one step CVD growth process using a polyferrocenylsilane block copolymer as the pre-organized catalyst source.

Supramolecular organometallic polymer chemistry: multiple morphologies and superstructures from the solution self-assembly of polyferrocene-block-polysiloxane-block-polyferrocene triblock copolymers.

The solution self-assembly of an organometallic-inorganic triblock copolymer, poly(ferrocenyldimethylsilane)-block-poly(dimethylsiloxane)-block-poly-(ferrocenyldimethylsilane) (PFDMS-b-PDMS-b-PFDMS, 3b; block ratio 1:13:1; Mn = 2.88 x 10(4) gmol(-1), polydispersity (PDI) 1.43 (gel permeation chromatography, GPC)) was studied in n-hexane, a PDMS block selective solvent. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and TEM with negative staining analysis of these micellar solutions after solvent evaporation revealed the presence of multiple micellar morphologies including spheres, cylinders, and novel flower-like supramolecular aggregates. TEM analysis of samples fractionated by ultracentrifugation and preparative size-exclusion chromatography suggest that the formation of multiple morphologies is a consequence of compositional variations. When micellar solutions were prepared at 50 degrees C (above the glass transition of the PFDMS core-forming block) flower-like micellar aggregates similar to those present in micellar solutions prepared at room temperature also formed. However, after solvent evaporation, TEM analysis of micellar solutions prepared in decane at about 150 degrees C, above the melt temperature of the PFDMS core (ca. 120-145 degrees C), revealed the presence of spherical micelles (when decane solutions at 150 degrees C were rapidly cooled to room temperature) and rod-like cylindrical micelles (when decane solutions at 150 degrees C were slowly cooled to room temperature). In contrast, poly(ferrocenylmethylethylsilane)block-poly(dimethylsiloxane)-block-poly(ferrocenylmethylethylsilane) (PFMES-b-PDMS-b-PFMES, 4; block ratio 1:16:1; Mn=2.90x10(4)g mol(-1), PDI= 1.42 (GPC)) and poly(ferrocenylmethylphenylsilane)-block-poly(dimethylsiloxane)-block-poly(ferrocenylmethylphenylsilane) (PFMPS-b-PDMS-b-PFMPS, 5; block ratio 1:15:1; Mn=3.00 x 10(4) gmol(-1), PDI = 1.38 (GPC)), which possess completely amorphous organometallic core-forming blocks, formed only spherical micelles in hexane at room temperature. These observations indicate that crystallinity of the insoluble polyferrocenylsilane block is a critical factor in the formation of the nonspherical micelle morphologies.