Crosslinking polyferrocenylsilanes

The use of highly crosslinked polyferrocenylsilane networks 3.48 x=y=0) leads to much improved ceramic yields (ca. 90%) and the pyrolytic formation of shaped, magnetic ceramics is efficient. The crosslinked network can be formed by heating the [l]silaferrocenophane, 3.47, in a mold (for 7 h at 150°C and then for 16 h at 180°C). The shape of the resulting crosslinked network 3.48 (x=y=0) resembles the mold used, such as a pentagon (Fig. 3.11). 

Tang and coworkers have reported that pyrolyzed hyperbranched polyferro-cenylsilanes have greater ceramic yields than their linear polymeric counterparts. Manners has reported that thermally crosslinked polyferrocenylsilanes (28) possessed greater thermal stability than their linear analogs. The swelling properties of these crosslinked polymers were examined, and the solubility parameter of the corresponding linear homopolymer was determined. The pyrolysis of linear, hyperbranched, and crosslinked polyferrocenylsilanes has resulted in the production of ceramics that possess magnetic properties. " ... 

A polymer gel based on an (inverse) opal was applied in order to obtain shorter switching times, which are also desirable for electrochemical color display purposes [346]. Hence, an all-color display was developed that, dependent on the applied potential, could reversibly switch between blue, green, red, and black. Here, crosslinked polyferrocenylsilane gels were partly swollen with glutaronitrile electrolyte. The degree of swelling was controlled electrochemically. Subsequently, the distance between the voids formed by the silica beads, which were etched by hydrofluoric acid treatment, could be altered. It should be mentioned that there are also other concepts for electrically switchable photonic crystals that are not directly connected to electrochemically induced solvation [347-349]. 

To initiate our studies of crosslinked polyferrocenylsilanes, we identified precursors 1 and 3 as candidates to form crosslinked networks consisting of linear segments of polymer 2. DSC studies of 3 indicated that this monomer undergoes exothermic ring-opening polymerization (ROP) at a fairly similar... 

Spirocyclic [Ijferrocenophanes have also been shown to thermally polymerize and these species function as crosslinking agents that allow access to polyferrocenylsilanes with controlled crosslink densities [67]. Amber, solvent-swellable gels are available by this route (see Section 3.3.6.4). The [l]dichlorosilaferrocenophane 3.23 represents a very useful precursor to [Ijferrocenophanes 3.24 with alkoxy (or amino) substituents, and subsequent ROP allows access to, for example, polyferrocenylalkoxy-silanes 3.25 (Eq. 3.11) [68]. In addition, polymers with Si-H or Si-Cl groups have been prepared, and these provide opportunities for post-polymerization modification by hydrosilylation and nucleophilic substitution, respectively [66]. 

Figure 16.11 TEM image in dark-field mode for shell-crosslinked cylinders of PFS53- -Pl32o block copolymers encapsulated with Ag nanoparticles. (Reprinted with permission from H. Wang, X. Wang, M.A. Winnik and I. Manners, Redox-mediated synthesis and encapsulation of inorganic nanoparticles in shell-cross-linked cylindrical polyferrocenylsilane block copolymer micelles, Journal of the American Chemical Society, 130, 12921, 2008. 2008 American Chemical Society.)...

By templating and crosslinking, tubuli with an electroactive interior were generated [166, 325]. These tubuli are still electrochemically active in organic solvent, although the interior polyferrocenylsilane is shielded by a rather thin poly (dialkylsiloxane) shell (Fig. 32). 

Fig. 32 Preparation pathway (top) for electroactive tubuli (TEM image bottom left), generated upon crosslinking of the shell. The polyferrocenylsilane is located along the inner wall, preventing electrode adsorption. Cyclic voltammograms are shown on the bottom right-, top CV crosslinked tubuli bottom CV diblock copolymer in common solvent, indicating adsorption processes (reprinted with permission from [166]. Copyright 2004 Wiley)...

Recently, we reported the first examples of well-characterized, crosslinked, swellable polyferrocenylsilanes (7). Thermal copolymerization of ferrocenophane 1 with the spirocyclic [IJferrocenophane 3 allows access to material with controlled crosslink densities. Because of the interesting properties of polyferrocenylsilanes, we identified crosslinked examples as possible candidates for stimuli-responsive gels. 

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