Manipulation and Deposition of Complex, Functional Block Copolymer Nanostructures using Optical Tweezers

Block copolymer self-assembly has enabled the creation of a range of solution-phase nanostructures with applications from optoelectronics and biomedicine to catalysis. However, to incorporate such materials into devices a method that facilitates their precise manipulation and deposition is desirable. Herein we describe how optical tweezers can be used to trap, manipulate, and pattern individual cylindrical micelles and larger hybrid micellar materials. Through the combination of TIRF imaging and optical trapping we can precisely control the three-dimensional motion of individual cylindrical block copolymer micelles in solution, enabling the creation of customizable arrays. We also demonstrate that dynamic holographic assembly enables the creation of ordered customizable arrays of complex hybrid block copolymer structures. By creating a program which automatically identifies, traps, and then deposits multiple assemblies simultaneously we have been able to dramatically speed up this normally slow process, enabling the fabrication of arrays of hybrid structures containing hundreds of assemblies in minutes rather than hours

Poly(ferrocenylmethylsilane): An Unsymmetrically Substituted, Atactic, but Semicrystalline Polymetallocene

Polyferrocenylsilanes (PFSs) [Fe­(μ-C₅H₄)₂SiRR′]_<i>n</i> are generally atactic and amorphous when unsymmetrically substituted at silicon (R ≠ R′) but are often able to crystallize if the substitution is symmetrical (R = R′). In this paper we report detailed studies of the ring-opening polymerization (ROP) of [1]­methylsilaferrocenophane Fe­(μ-C₅H₄)₂SiMeH (<b>1</b>) by thermal, anionic and photolytic methods to yield an unsymmetrically substituted yet crystallizable poly­(ferrocenylmethylsilane) (<b>PFMS</b>) (R = Me, R′ = H) with Me and H substituents at silicon (designated <b>PFMS</b>_<b>T</b>, <b>PFMS</b>_<b>A</b>, and <b>PFMS</b>_<b>P</b>, respectively). The structures of the resulting polymers were shown to possess significant differences as revealed by MALDI–TOF mass spectroscopy experiments. For example, <b>PFMS</b>_<b>A</b> prepared using <i>n</i>-BuLi as an initiator was shown to contain cyclic contaminants whose formation indicated the existence of backbiting reactions during polymer chain growth. On the other hand, photolytic ROP of <b>1</b> using Na­[C₅H₅] as an initiator led only to the formation of linear material but was not a living process due to side reactions between the initiator (and presumably the propagating polymeric anions) and the Si–H groups in the monomer <b>1</b>. Transition metal-catalyzed ROP of <b>1</b> was also explored and, in contrast, was found to afford a hyperbranched and amorphous low molar mass polyferrocenylsilane (<b>4</b>), presumably also as a result of side reactions involving the Si–H groups in the monomer. High resolution ¹H and ¹³C NMR spectroscopic studies revealed that <b>PFMS</b>_<b>T</b>, <b>PFMS</b>_<b>A</b>, and <b>PFMS</b>_<b>P</b> were all atactic, irrespective of the polymerization route utilized. The crystallization of the samples was investigated by wide-angle X-ray scattering (WAXS), which showed a reflection corresponding to a <i>d</i>-spacing of 6.32 Å, by differential scanning calorimetry (DSC), which revealed melting endotherms in the range 106–139 °C, and by polarizing optical microscopy (POM)

Synthesis and Bulk Self-Assembly of ABC Star Terpolymers with a Polyferrocenylsilane Metalloblock

The synthesis, characterization, and self-assembly of a range of ABC star polymers with arms of polyisoprene, poly­(ferrocenylethylmethylsilane), and polystyrene is reported. A library of azide-functionalized polyisoprene and poly­(ferrocenylethylmethylsilane) homopolymers were prepared by living anionic polymerization. Polystyrene was synthesized by living anionic polymerization and quenched with 3-triisopropylsilylethynyl-5-trimethylsilylethynylbenzaldehyde, yielding “core-functionalized” polystyrene with two different alkyne units. The azide-functionalized monomers were sequentially attached to core-functionalized polystyrene via copper­(I)-catalyzed azide–alkyne cycloaddition reactions, giving polystyrene–polyisoprene–poly­(ferrocenylethylmethylsilane) ABC star terpolymers with different compositions and narrow dispersities. Additionally, a chlorosilane route was employed as an alternative means of synthesis. Bulk films of each star terpolymer were prepared, and their self-assembly was analyzed by transmission electron microscopy. The formation of a diverse range of morphologies was observed, including lamellae with alternating cylinders and two different Archimedean tiling patterns

Synthesis and the Thermal and Catalytic Dehydrogenation Reactions of Amine-Thioboranes

A series of trimethylamine-thioborane adducts, Me₃N·BH₂SR (R = <i>t</i>Bu [<b>2a</b>], <i>n</i>Bu [<b>2b</b>], <i>i</i>Pr [<b>2c</b>], Ph [<b>2d</b>], C₆F₅ [<b>2e</b>]) have been prepared and characterized. Attempts to access secondary and primary amine adducts of thioboranes via amine-exchange reactions involving these species proved unsuccessful, with the thiolate moiety shown to be vulnerable to displacement by free amine. However, treatment of the arylthioboranes, [BH₂–SPh]₃ (<b>9</b>) and C₆F₅SBH₂·SMe₂ (<b>10)</b> with Me₂NH and <i>i</i>Pr₂NH successfully yielded the adducts Me₂NH·BH₂SR (R = Ph [<b>11a</b>], C₆F₅ [<b>12a</b>]) and <i>i</i>Pr₂NH·BH₂SR (R = Ph [<b>11b</b>], C₆F₅ [<b>12b</b>]) in high yield. These adducts were also shown to be accessible via thermally induced hydrothiolation of the aminoboranes Me₂NBH₂, derived from the cyclic dimer [Me₂N-BH₂]₂ (<b>13</b>), and <i>i</i>Pr₂NBH₂ (<b>14</b>), respectively. Attempts to prepare the aliphatic thiolate substituted adducts R₂NH·BH₂SR′ (R = Me, <i>i</i>Pr; R′ = <i>t</i>Bu, <i>n</i>Bu, <i>i</i>Pr) via this method, however, proved unsuccessful, with the temperatures required to facilitate hydrothiolation also inducing thermal dehydrogenation of the amine-thioborane products to form aminothioboranes, R₂NBH­(SR′). Thermal and catalytic dehydrogenation of the targeted amine-thioboranes, <b>11a</b>/<b>11b</b> and <b>12a</b>/<b>12b</b> were also investigated. Adducts <b>11b</b> and <b>12b</b> were cleanly dehydrogenated to yield <i>i</i>Pr₂NBH­(SPh) (<b>22</b>) and <i>i</i>Pr₂NBH­(SC₆F₅) (<b>23</b>), respectively, at 100 °C (18 h, toluene), with dehydrogenation also possible at 20 °C (42 h, toluene) with a 2 mol % loading of [Rh­(μ-Cl)­cod]₂ in the case of the former species. Similar studies with adduct <b>11a</b> evidenced a competitive elimination of H₂ and HSPh upon thermolysis, and other complex reactivity under catalytic conditions, whereas the fluorinated analogue <b>12a</b> was found to be resistant to dehydrogenation

Crystallization-Driven Solution Self-Assembly of μ‑ABC Miktoarm Star Terpolymers with Core-Forming Polyferrocenylsilane Blocks

A comparative study of the solution self-assembly behavior of two polystyrene-<i>arm</i>-polyisoprene-<i>arm</i>-polyferrocenylsilane (μ-SIF) miktoarm star terpolymers of similar composition has been conducted: one with a short, atactic, noncrystallizable poly­(ferrocenylethylmethylsilane) (PFEMS) block (μ-SIF_a) and one with a short, crystallizable poly­(ferrocenyldimethylsilane) (PFDMS) block (μ-SIF_c). Both solvent composition and the amorphous/crystallizable nature of the polyferrocenylsilane (PFS) block exhibited a profound influence on the morphologies of the micelles obtained. In hexane, the formation of uniform spherical micelles with an amorphous, phase-mixed PS/PFS core was observed for both μ-SIF_a and μ-SIF_c. The introduction of cyclohexane (a theta-solvent for PS at 34.5 °C) to give a 1:1 cyclohexane/hexane (v/v) solvent composition resulted in the formation of distorted spherical micelles with a core composed of phase-separated PS and PFS, for both μ-SIF_a and μ-SIF_c. Interestingly, the distorted spherical micelles formed from crystallizable μ-SIF_c evolved with time into elongated fiber-like structures with a phase-separated PS and PFDMS core, while the noncrystallizable counterpart, μ-SIF_a, remained as distorted spheres. It was found that in ethyl acetate, a good solvent for PI and PS, μ-SIF_a remained unimeric in solution, whereas μ-SIF_c formed cylindrical micelles composed of a crystalline PFDMS core and a phase-separated, patchy, PS and PI corona. Finally, seeded growth of μ-SIF_c from short, cylindrical PFDMS-<i>b</i>-PDMS seeds (PDMS = polydimethylsiloxane) was demonstrated, yielding B–A–B block comicelles where outer segments derived from μ-SIF_c blocks bore a strong resemblance to that ultimately formed under conditions of homogeneous nucleation

Multifunctional Block Copolymer: Where Polymetallic and Polyelectrolyte Blocks Meet

Sequential reversible addition–fragmentation transfer (RAFT) polymerization of a mixed sandwich cobaltocene monomer (η⁵-cyclopentadienyl-cobalt-η⁴-cyclobutadiene (CpCoCb)) and a phosphonium salt functionalized styrene monomer resulted in the first example of a unique multifunctional block copolymer consisting of a metallopolymer block and a polyelectrolyte block. The polyelectrolyte block was decorated with a gold anion (AuCl₄^–) via salt metathesis, resulting in a heterobimetallic block copolymer with distinct gold and cobalt sections. Solution self-assembly behavior of this unique metallopolymer-<i>b</i>-polyelectrolyte copolymer before and after salt metathesis was studied. Heterobimetallic micelles with a gold containing core and a cobalt-containing corona were obtained, and then the core was reduced to form gold nanoparticles (AuNPs). Studies on the solid-state self-assembly of this unique block copolymer showed that it phase separated into hexagonally packed cylinders. Salt metathesis of the phase-separated block copolymers was utilized as the first example of a nonstandard selective staining method to exclusively stain the polyelectrolyte domains with the AuCl₄^– anion. Staining the metallopolymer domain by RuO₄ provided the complementary pattern. Pyrolysis of the self-assembled block copolymers resulted in magnetic cobalt-phosphate nanoparticles with 17% char yield

Reversible Cross-Linking of Polyisoprene Coronas in Micelles, Block Comicelles, and Hierarchical Micelle Architectures Using Pt(0)–Olefin Coordination

Previous work has established that polyisoprene (PI) coronas in cylindrical block copolymer micelles with a poly(ferrocenyldimethylsilane) (PFS) core can be irreversibly cross-linked by hydrosilylation using (HSiMe₂)₂O in the presence of Karstedt’s catalyst. We now show that treatment of cylindrical PI-<i>b</i>-PFS micelles with Karstedt’s catalyst alone, in the absence of any silanes, leads to PI coronal cross-linking through Pt(0)–olefin coordination. The cross-linking can be reversed through the addition of 2-bis(diphenylphosphino)ethane (dppe), a strong bidentate ligand, which removes the platinum from the PI to form Pt(dppe)₂. The Pt(0) cross-linking of PI was studied with self-assembled cylindrical PI-<i>b</i>-PFS block copolymer micelles, where the cross-linking was found to dramatically increase the stability of the micellar structures. The Pt(0)–alkene coordination-induced cross-linking can be used to provide transmission electron microscopy contrast between PI and poly(dimethylsiloxane) (PDMS) corona domains in block comicelles as the process selectively increases the electron density of the PI regions. Moreover, following the assembly of a hierarchical scarf-shaped comicelle consisting of a PFS-<i>b</i>-PDMS platelet template with PI-<i>b</i>-PFS tassels, Pt(0)-induced cross-linking of the PI coronal regions allowed for the selective removal of the PFS-<i>b</i>-PDMS center, leaving behind an unprecedented hollowed-out scarf structure. The addition of Karstedt’s catalyst to PI or polybutadiene homopolymer toluene/xylene solutions resulted in the formation of polymer gels which underwent de-gelation upon the addition of dppe

Zirconium-Catalyzed Imine Hydrogenation via a Frustrated Lewis Pair Mechanism

Zirconium-based frustrated Lewis pairs (FLPs) are active imine hydrogenation catalysts under mild conditions. Complexes of the type [Cp^R₂ZrOMes]­[B­(C₆F₅)₄] utilize the imine substrate itself as the Lewis base component of the FLP. Catalyst performance is a function of ligand structure; in general more bulky, more electron rich cyclopentadienyl derivatives give the best results. However, Cp* derivatives are not catalytically active, being stable after initial heterolytic cleavage of H₂; this allows experimental verification of the competence of the zirconocene–imine pair in FLP-type heterolytic H₂ cleavage. Enamines and protected nitriles are also hydrogenated if an additional internal phosphine base is used

Facile Formation of FePd Nanoparticles from Single-Source [1]Ferrocenophane Precursors

Mixed-metal FePd alloy nanoparticles (NPs) have been synthesized in moderate yield (ca. 55–60%) and at relatively low temperatures from single-source [1]­ferrocenophane precursors. Thermolysis of [Fe­(η⁵-C₅H₄)₂­Pd­(P<i>n</i>Bu₃)₂] (<b>7</b>) (1 h, 150 °C) and the new species [Fe­(η⁵-C₅H₄)₂­Pd­{P<i>n</i>Bu₂­(CH₂)₄­P<i>n</i>Bu₂}] (<b>9</b>) (1 h, 190 °C) afforded crystalline, heterobimetallic FePd alloy NPs with diameters of ca. 4 nm (<b>11</b>) and 3.5 nm (<b>12</b>), respectively, together with mixtures of unidentified, mainly ligand-derived products. Both sets of particles were analyzed by high resolution transmission electron microscopy, which, in addition to providing particle size, determined the spacing between the lattice fringes to be 0.23 nm. Evidence for the formation of alloy nanoparticles, rather than a mixture of those comprising pure metals, was obtained by energy-dispersive X-ray analysis, which confirmed the presence of both Fe and Pd in a single particle. This assertation was further supported by wide-angle X-ray scattering of <b>11</b> and <b>12</b>, which displayed broad reflections at 2θ = 40.58° and 40.09°, respectively, in good agreement with previous studies of FePd NPs. Atomic absorption spectroscopy was employed for bulk analysis of the particles and indicated that that the compositions of <b>11</b> and <b>12</b> were ca. Fe₃₅Pd₆₅

Monitoring Collapse of Uniform Cylindrical Brushes with a Thermoresponsive Corona in Water

We generated rod-like micelles of uniform length by living crystallization-driven self-assembly of a polyferrocenylsilane (PFS) block copolymer PFS₂₆-<i>b</i>-POEGMA₁₆₃ in a methanol–ethanol mixture and then transferred these micelles to water. The corona chains consisted of poly­(oligoethylene glycol methacrylate) that had a lower critical solution temperature (LCST) of 40.5 °C in water. We used a combination of static (SLS) and dynamic (DLS) multiangle light scattering to determine the dimensions of these cylindrical brush micelles in solution. Measurements carried out in dilute solution in water over a series of temperatures from 23 to 50 °C showed that the collapse transition was broad and continuous, upon both heating and cooling. This response is different from the collapse transition of POEGMA₁₆₃ homopolymer in water, which occurs over a very narrow temperature range. Thus, we show that the collapse transition of a cylindrical brush has important features in common with the collapse of a brush of thermoresponsive polymers on a planar surface