Living polymerizations involve the creation of polymer chains without significant irreversible chain transfer or chain termination. Such processes are widely used to access well-defined macromolecular materials with controlled architectures, such as block and star polymers. Although this concept was first realized for anionic polymerizations in the 1950s, many key recent advances have been made, most notably in the area of radical polymerization. Here, we report a living photopolymerization that involves photoexcited monomers. Exposure of metal-containing ferrocenophane monomers to Pyrex-filtered light from a mercury lamp (lambda>310 nm) or to bright sunlight in the presence of an anionic initiator leads to living polymerizations, in which the conversion and molecular weight of the resulting polymer can be controlled by the irradiation time. Photoirradiation selectively weakens the iron-cyclopentadienyl bond in the monomer, allowing the use of moderately basic and highly functional-group-tolerant initiators. The polymerization proceeds through attack of the initiator and propagating anion on the iron atom of the photoexcited monomer and, remarkably, the polymerization rate decreases with increasing temperature. Block copolymer formation is possible when the light source is alternately switched on and off in between sequential addition of different monomers, providing unprecedented, photocontrolled access to new types of functional polymers.

Living anionic ring-opening (ROP) polymerization of ethylmethylsila[1]ferrocenophane yields atactic poly(ferrocenylethylmethylsilane) (PFEMS) homopolymers with controlled molecular weights (M n = 4000−41 400) and narrow molecular weight distributions (PDI = 1.01−1.02). A series of well-defined polystyrene-block-poly(ferrocenylethylmethylsilane) (PS-b-PFEMS) diblock copolymers was synthesized from styrene and ethylmethylsila[1]ferrocenophane via sequential anionic polymerization. The iron content was readily varied (PFEMS volume fraction = 0.07−0.68), affording high molecular weight (M n = 38 700−149 000) iron-rich diblock copolymers with narrow molecular weight distributions (PDI = 1.00−1.07). Both the PFEMS homopolymers and the PS-b-PFEMS diblock copolymers were shown to be amorphous due to the atactic nature of the organometallic block. As a result, PS-b-PFEMS block copolymers readily undergo solid-state self-assembly in the bulk. A spectrum of nanometer-sized iron-rich morphologies has been accessed, and in many cases these arrays were found to be well-ordered over large areas.

The glancing angle deposition (GLAD) technique is used to fabricate nanostructured thin films with high surface area. Quantifying this property is important for optimizing GLAD-based device performance. Our group has used high-sensitivity krypton gas adsorption and the complementary technique of cyclic voltammetry to measure surface area as a function of deposition angle, thickness, and morphological characteristics for several metal oxide thin films. In this work, we studied amorphous titanium dioxide (TiO(2)), amorphous silicon dioxide (SiO(2)), and polycrystalline indium tin oxide (ITO) nanostructures with vertical and helical post morphologies over a range of oblique deposition angles from 0 to 86 degrees. Krypton gas sorption isotherms, evaluated using the Brunauer-Emmettt-Teller (BET) method, revealed maximum surface area enhancements of 880 +/- 110, 980 +/- 125, and 210 +/- 30 times the footprint area (equivalently 300 +/- 40, 570 +/- 70, and 50 +/- 6 m(2) g(-1)) for vertical posts TiO(2), SiO(2), and ITO. We also applied the cyclic voltammetry technique to these ITO films and observed the same overall trends as seen with the BET method. In addition, we applied the BET method to the measurement of helical films and found that the surface area trend was shifted with respect to that of vertical post films. This revealed the important influence of the substrate rotation rate and film morphology on surface properties. Finally, we showed that the surface area scales linearly with film thickness, with slopes of 730 +/- 35 to 235 +/- 10 m(2) m(-2) microm(-1) found for titania vertical post films deposited at angles from 70 to 85 degrees. This characterization effort will allow for the optimization of solar, photonic, and sensing devices fabricated from thin metal oxide films using GLAD.

In depth studies of the use of electron transfer reactions as a means to control the self-assembly of diblock copolymers with an electroactive metalloblock are reported. Specifically, the redox-triggered self-assembly of a series of polystyrene-block-polyferrocenylsilane (PS-b-PFS) diblock copolymers in dichloromethane solution is described. In the case of the amorphous polystyrene(n)-b-poly(ferrocenylphenylmethylsilane)(m) diblock copolymers (PS(n)-b-PFMPS(m): n = 548, m = 73; n = 71, m = 165; where n and m are the number-averaged degrees of polymerization), spherical micelles with an oxidized PFS core and a PS corona were formed upon oxidation of more than 50% of the ferrocenyl units by [N(C(6)H(4)Br-4)(3)][SbX(6)] (X = Cl, F). Analogous block copolymers containing a poly(ferrocenylethylmethylsilane) (PFEMS) metalloblock, which has a lower glass transition temperature, behaved similarly. However, in contrast, on replacement of the amorphous metallopolymer blocks by semicrystalline poly(ferrocenyldimethylsilane) (PFDMS) segments, a change in the observed morphology was detected with the formation of ribbon-like micelles upon oxidation of PS(535)-b-PFDMS(103) above the same threshold value. Again the coronas consisted of fully solvated PS and the core consisted of partially to fully oxidized PFS associated with the counteranions. When oxidation was performed with [N(C(6)H(4)Br-4)(3)][SbF(6)], reduction of the cores of the spherical or ribbon-like micelles with [Co(η-C(5)Me(5))(2)] enabled full recovery of the neutral chains and no significant chain scission was detected.

In this communication we study the influence of strong 3D confinement on the self-assembly of diblock copolymers containing a polyferrocenylsilane metallopolymer segment. Both silica colloidal crystals and silica inverse colloidal crystals, having nanometer-scale interconnected pore networks, are used as molds to direct the self-assembly. Unusual morphologies, such as concentric shells and branched lamellae, result from the interaction of the polymer with the high surface area topologically periodic templates.

Carbon nanotubes (CNTs), with their exceptional electrical properties, chemical stability, and mechanical strength, have attracted a great deal of attention. This makes the material attractive for a wide range of applications, including composite materials, 1 battery electrode materials, 2 nanoelectronics, 3,4 and nanoscale sensors. 5 However, the properties of CNTs are highly dependent on their structure and size. Such sensitivity to size and structure imposes a potential barrier to the realization of the novel properties of CNTs in many applications. In the growth of CNTs by chemical vapor deposition (CVD), the diameters of CNTs are determined by the sizes of catalysts. 6 One way to obtain CNTs with fewer chiral arrangements is to use smaller catalyst particles. Thus, CNTs with smaller diameters, for example less than 2 nm, are most likely to be single-walled with fewer geometrical arrangements. This should limit the band gap range and allow the possibility of having all metallic or all semiconducting CNTs from a given growth. Moreover, such small-diameter nanotubes have larger band gaps, which minimize off-state leakage, thereby increasing the transistor on/off current ratio in transistor applications. 7 Significant progress has been made in driving catalyst size, and thus nanotube diameters, down

We report the creation and properties of colloidally stable shell-cross-linked cylindrical organometallic block copolymer micelles with adjustable length and swellability. The one-dimensional (1D) structures with semicrystalline polyferrocenylsilane (PFS) cores and polyisoprene (PI) coronas were initially self-assembled from PI-b-PFS block copolymers in a PI-selective solvent such as hexane. The length of the cylinders could be varied from hundreds of nanometers to several tens of micrometers by adjusting solution conditions, using various solvents such as hexane, decane, or hexane/THF (or toluene) mixtures. The cylindrical micelles with vinyl groups in the PI corona were cross-linked through a Pt(0)-catalyzed hydrosilylation reaction using 1,1,3,3-tetramethyl disiloxane as a cross-linker at room temperature. The shell cross-linking significantly increased the stability of the micelles relative to the un-cross-linked precursors as no fragmentation was observed upon sonication in solution. In addition, the structural integrity of the micelles was also enhanced after solvent removal; a solid sample was successfully microtomed and then examined using TEM, which revealed circular cross-sections for the PI-b-PFS micelles with an average diameter of ca. 15 nm. We also discovered that shell cross-linking is a prerequisite for generating ceramic replicas through the pyrolysis of PI-b-PFS aggregates. Moreover, we were able to pattern the cross-linked micelles on a flat substrate by microfluidic techniques, generating perpendicularly crossed lines of aligned micelles. In short, the shell-cross-linked PI-b-PFS 1D organometallic aggregates are a promising new type of nanomaterial with intriguing potential applications.

The pyrolysis of cylinder-forming samples of the diblock copolymer polystyrene-block-poly(ferrocenylethylmethylsilane) (PS-b-PFEMS) in bulk and in thin films has confirmed that these materials are useful for the generation of semi-ordered arrays of C/SiC ceramics containing Fe nanoparticles which are derived from the organometallic domains. In many cases, the ceramic mass yields were predictable and produced ceramics bearing a monomodal distribution of iron nanoparticles due to the nanoscaled structure of the preceramic PFEMS domains. The pyrolysis of thin films stabilized by cross-linking the PS domains with UV light demonstrated high areal yields, improved shape retention, and the presence of cylinder-centered magnetic nanoparticles.