Gram‐Scale Synthesis of Submicrometer‐Long Polythiophene Wires in Mesoporous Silica Matrices

Abstract

The mesoporous silica MCM-41 is characterized by ordered hexagonal arrays of uniform channels. The pore diameter can be controlled in the range of 2-10 nm by the synthetic procedures and the surface area is about 1000 m 2 g À1 . [1][2] These attributes make the material attractive not only as sorbent, catalytic support, and separation membrane, but also as ideal host for rational nanomanufacturing, [3][4][5][6][7] especially as synthetic scaffolds for controlled polymerization. [8][9][10][11][12][13] Polyanilin and polyacryl fibers were first synthesized inside MCM-41 by oxidation and free-radical initiation of the corresponding monomers. [8][9] Contactless microwave conductivity measurements displayed a high conductivity of the encapsulated polymer as compared with the bulk polymer. Since then the polymerization of various monomers, such as styrene, alkyne, ethylene, and methylmethacrylate, have been reported within MCM-41. [3][4][5][6][7][8][9][10][11][12][13] The described polymerization processes occur in two steps, 1) loading of the monomer into preformed silica channels by chemical vapor deposition (CVD) or freeze-thaw cycles, and 2) polymerization by irradiation or oxidation.It is conceivable that the structure-directing agents for the silicate, for example, cetyltrimethylammonium bromide, could also bear polymerizable units. Aida and Tajima applied this approach on polyacetylene, but obtained only a few macroscopic rods, with diameters between 15 and 25 mm. [13] We assumed that flexible thiophene units with pentyl or undecyl ammonium side chains may form more fluid, densely packed template monomers and could be directly polymerized in situ in a controllable fashion to linear macromolecular fibers. Using this strategy (Figure 1), we report herein the fabrication of submicrometer long conjugated polythiophene molecular wires of molecular thinness in gram-scale. The surfactants, which function both as template and monomer, trimethyl-(11-thiophen-3-yl-undecyl) ammonium bromide (2) and the pentyl homologue 1 were synthesized by standard methods.[14] Mesostructured silicates were synthesized following a slightly modified procedure reported by Ozin et al. for the preparation of mesoporous silica with functional organic groups within the channels.[15] In a typical synthesis, 1.0 g of tetraethylorthosilicate (TEOS) was added to an aqueous solution of NH 4 OH containing monomer 2 under stirring. The molar ratio of 1.0 Si:114 H 2 O:8.0 NH 4 OH (28 %):0.12 thiophene 2 was thus established in the reaction mixture. After 60 min stirring at room temperature, the solution was left standing at 90 8C for 5 h in a closed polyethylene bottle. A white powder was collected by filtration, washed thoroughly with millipore water, and dried in air. The yield was about 1 g. We assume that all of the thiophene 2 was entrapped in the material, because the filtrate seemed not to contain a detergent. The homologous monomer 1 was less useful as a template, presumably, because of its shorter chain length, it does not form micelles. Figur...

A Mesoporous/Crystalline Composite Material Containing Tin Phosphate for Use as the Anode in Lithium‐Ion Batteries

“…The presence of substantial amounts of other "spectator atoms", such as the B and P atoms in Sn 2 BPO 6 , apparently prevents Sn aggregation. [2] However, these materials show an initial capacity of about 500 mA h g À1 , with a relatively high irreversible capacity of about 500 mA h g À1 during the first cycle.…”

“…Figure 1 shows small-angle X-ray scattering (SAXS) patterns of the mesoporous tin phosphates prepared in the presence of cetyltrimethylammonium bromide (CTAB, CH 3 (CH 2 ) 15 N(CH 3 ) 3 Br) as a structure-directing agent, before and after annealing at 400 8C for 8 h. The three resolved peaks indexed as (100), (110), and (200) confirm a well-ordered hexagonal mesoporous structure. [6,7] The intense (100) peak at 2q = 2.188 AE 0.098 of the as-synthesized mesoporous tin phosphate corresponds to a d spacing of 4.0 AE 0.2 nm (from 2d sin q = l), with a nearest-neighbor distance of 4.7 AE 0.2 nm. The high-angle XRD pattern shown in the inset of Figure 1 a indicates the formation of crystalline SnHPO 4 with a space group P2 1 /c (monoclinic).…”

Challenges and breakthroughs in recent research on self-assembly

“…In contrast, the two-dimensional lamellar phase afforded spatial freedom for electron recombination. Similarly thiophene polymerization in mesoporous silica channels was reported by Fuhrhop and coworkers [332]. Supramolecular self-assemblies can also be confined in mesopores.…”

Polythiophene microspheres synthesized by transition metal mediated oxidative dispersion polymerization

“…[6][7][8][9][10][11][12][13][14][15] One of the most convenient synthetic procedures is the heterogeneous oxidative polymerization of thiophene in organic solvents, traditionally with the aid of commercially available small molecule surfactants. Recently Li et al…”