Poly ferrocenylsilane s

The relief of ring-strain present in silicon-bridged ferrocenophanes can be utilized as the driving foree for its ring-opening polymerization (ROP). Manners and coworkers have shown that it is possible to induce the ROP of silicon-bridged ferrocenophanes by at least three different synthetic approaches [3,7,44-46], These are (a) thermal ROP (b) anionic ROP and (c) transition-metal-complex eatalyzed ROP. 

1 Thermal Ring-opening Polymerization of Silicon-bridged Ferrocenophanes 

Using the thermal ROP methodology a large number of poly(ferrocenylsilane)s have been prepared. Representative examples are shown in Fig. 8.15. The range of substituents on silicon that can be present 

Poly(ferrocenylsilane)s that contain reactive chlorine groups can be used for further elaboration (Fig.8.16). 

Thermal ROP can also be used for copolymerizing the cycloferrocenyl-silane with other strained rings such as cyclotetrasilanes. Thus, heating a 1 1 mixture of [Fe(Ti C5H4)2SiMe2] and [MePhSi]4 at 150 °C affords a random copolymer (Fig. 8.17) [50]. 

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Water-soluble poly(ferrocenylsilane) polycations, belonging to the rare class of main chain organometallic polyelectrolytes, have been reported by us and others [35,36,87,88]. These compounds are of interest because they combine the imusual properties of poly(ferrocenylsilane)s with the processabiUty of polyelectrolyte solutions—for example, enabling one to make use of ionic interactions to deposit these polymers onto substrates. Polyelectrolytes can be employed in layer-by-layer self-assembly processes to form ultrathin multilayer films with controlled thickness and composition [89,90]. 

Although cationic poly(ferrocenylsilane)s have been used in combination with commercially available organic polyanions to fabricate heterostruc-tured multilayer films [36,37], fuUy organometallic multilayers were not reported until recently due to the lack of availability of anionic organometallic polyions [94,95]. Multilayer structures composed of poly(ferrocenylsilane)... 

Cyclic, silicon-bridged [l]ferrocenophanes have been found to undergo thermal ring-opening polymerization to afford high-molecular-wei t poly(ferrocenylsilane)s (see Eq. 1.31) [8, 43]. Many other members of this family of polymers are now known including those where the silicon center is replaced by Sn(IV), P(III), Ge(IV), B(III) etc., [8],... 

Organometallic polymers such as poly(ferrocenylsilane)s have been shown to be precursors for new types of magnetic ceramics [9, 42]. Similarly poly(silyleneethylene)s [41] and some polysilanes are polymeric precursors for silicon carbide ceramics [19]. 

Properties and Applications of Poly(ferrocenylsilane)s and Related Polymers... 

Poly(ferrocenylsilane)s are high-molecular-weight polymers. The molecular weights of polymers prepared by the thermal ROP range from 10 to 10 with polydispersity indices of 1.5-2.5 [3, 7, 44-46], The molecular weights of the polymers prepared by the anionic polymerization method can be controlled by varying the amount of initiator. Further, polymers with narrow PDFs (less than 1.3) can be obtained by the anionic polymerization [3]. 

The Si-NMR chemical shifts of various types of poly(ferrocenylsilane)s are summarized in Table 8.3. The presence of oxygen substituents moves the chemical shifts upfield in comparison to alkyl substituents. But it can be seen that most chemical shifts span a fairly narrow range. 

Table 8.3. Si NMR and Tg data for some selected poly(ferrocenylsilane)s...

Poly(ferrocenylsilane)s have been investigated extensively in terms of their electrochemical behavior. The general observation of these investigations is that under cyclic voltammetric conditions these polymers show two reversible oxidation (Fe(II)/Fe(III)) peaks separated by a AE1/2 that varies from about 0.16 to 0.29 V. The observation of two oxidation peaks has been explained as two successive events where the first oxidation involves a set of alternate ferrocene units followed by the second oxidation of the other alternate set. The second oxidation occurs at a higher potential than the first one [3,7]. 

Unlike polysilanes, poly(ferrocenylsilane)s do not have electron delocalization in their backbone. The electronic absorption of these polymers is typical of those known for unstrained ferrocene derivatives. The monomer ferrocenophanes, on the other hand, show bathochromic absorption (470-480 nm) in comparison to bis-trimethylsilylferrocene (448 nm) [44-46]. 

The structure of crystalline poly(ferrocenylsilane)s have attracted attention. Studies on model eompounds have also been earried out to augment the imderstanding of the polymeric derivatives. These studies reveal that polymers such as [Fe(ri -C5H4)2SiMe2]n have ra s-planar structures [61]. 

Poly(ferrocenylsilane)s are being investigated as organometallic polyelectrolytes [63]. These can be prepared by stepwise synthetic procedures (Figs. 8.30 and 8.31). 

Kutnyanszky, E., Hempenius, M. A., Vancso, G. J. (2014). Polymer bottlebrushes with a redox responsive backbone feel the heat synthesis and characterization of dual responsive poly(ferrocenylsilane)s with PNIPAM side chains. Polymer Chemistry. 

Kulbaba, K, MacLachlan, M.J., Evans, C.E.B., and Manners, 1. (2001) Organometallic gels characterization and electrochemical studies of sweUable, thermally crosslinked poly(ferrocenylsilane)s. Macromolecular Chemistry and Physics, 202,1768. 

Kulbaba K, MacLachlan Ml, Evans CEB, Manners L (2001) Organometallic gels characterization and electrochemical studies of swellable, thermally taosslinked poly (ferrocenylsilane)s. Macromol Chem Phys 202 1768-1775... 

Sui X, Shui L, Cui J, Xie Y, Song J, van den Berg A, Hempenius Mark A, Julius Vancso G (2014) Redox-responsive organometallic microgel particles prepared from poly (ferrocenylsilane)s generated using microfluidics. Chem Commun 50 3058-3060... 

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