Ferrocene-containing polymers

Poly(dihexylgermane) and poly(dioctylgermane) are strongly thermo-chromic. For example, a thin film of [nHex2Ge]n absorbs at -11 °C at 370 nm, while at 22 °C the absorption shifts to 337 nm [12], These changes are reversible as a function of temperature. On the other hand, poly(diarylstannane)s do not seem to be thermochromic, although poly(dialkylstannane)s are thermochromic [18-20]. 

Ferrocene is both thermally and electrochemically very robust. These properties have motivated attempts to incorporate the ferrocene unit as part of a polymer framework. This section deals with various types of polymers containing ferrocene. 

Oskar Nuyken,VoIker Burkbardt, Thomas Pohhnann, Max Herberhold, Fred Jochen Litterst, and Christian Hiibsch 

This field of activity can be seen as crossing the conventional boundaries of organic, inorganic, and polymer chemistry as well as physics and material science. 

The aim of our work was the synthesis of tailor-made polymers containing ferrocene units at different positions of the polymer chain. 

From Moflbauer spectroscopy of ferrocene-labelled polymers one coidd expect valuable information about the polymer structure, diffusion, and fluctuation processes. In earlier experiments we have been able to show remarkable differences in MoBbauer spectra taken from solvent-free and swollen polymers [6]. 

Basically there are two strategies for the synthesis of metal-containing polymers. One approach is to synthesize derivatives of organic polymers. The second pathway involves the conversion of monomeric ferrocenes into polymers. We have concentrated on the latter approach. 

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Properties of ferrocene-containing polymers have been improved by inclusion of pyrazole systems in the backbone. The synthesis of (748) was achieved by condensation of bis()3-diketoferrocenes) with aromatic dihydrazines to give polyhydrazones that were later cyclo-dehydrated (B-80MI40408). 

Germanium-bridged [l]ferrocenophanes undergo a number of ring-opening polymerization reactions to yield ferrocene-containing polymers, and the versatility of this interconversion has been reviewed. A -GeMe2-... 

The landmark discovery of ferrocene by Kealy and Paulson in 1951 marked the beginning of modern organometallic chemistry. The first organometallic addition polymer was polyvinyl-ferrocene synthesized by Arimoto and Haven in 1955. While polyvinylferrocene (structure 11.32) had been synthesized it was about another decade until the work of Pittman, Hayes, and George, and Baldwin and Johnson allowed a launch of ferrocene-containing polymers. 

A number of organometallic polymers containing metallocenes and metallocene analogues has been well-known for some time2. Because of the features of high-temperature stability and radiation resistance of the ferrocene nucleus, ferrocene-containing polymers are of special interest. Basically, these polymers may be divided into two classes the metallocene moiety is either located in a pendant group or in a backbone of the polymer chain. The former polymers have been synthesized by vinyl polymerization of vinyl metallocene monomers such as vinylferrocene. The latter polymers have been prepared by polycondensation of l,l -disubstituted metallocenes or metallocene dihalides with a.w-disubstituted monomers, and fell into two main types, (A) and (B). 

Thermal stability of the vinyl ferrocene and ferrocene containing polymers plus unmodified polymer and neat ferrocene controls was determined by thermal gravimetric analysis at a heating rate of 10 /mln. The results are depicted in Figure 4. Apparently vinyl ferrocene imparts greater thermal stability to the BA/S/MAA polymer than the ferrocene additive. In fact, 1% vinyl ferrocene allows about a 50 C additional rise in temperature before decomposition relative to the unmodified polymer. Curiously, a substantial exotherm is present at 400 - 450 C (bump on curve) for the vinyl ferrocene modified polymers, but does not appear for the ferrocene modified polymers. 

Ozaki, J., Mitsui, M. and Nishiyama, Y., Carbonization of ferrocene containing polymers and their electrochemical properties. Carbon 36(1-2) (1998) pp.l31-13S. 

Multienzyme systems have been used in carbon paste electrodes, providing bio-catalytic cascades that result in an analytical amperometric signal. For example, acetylcholine esterase (AChE) and choline oxidase (ChOx) have been co-immobilized in carbon pastes, either with monomeric TTF [145] or flexible ferrocene-containing polymers [146] as electron mediators. The primary reaction includes the hydrolysis of acetylcholine biocatalyzed by AChE, then the choline produced is oxidized by the electrically contacted ChOx giving an analytical amperometric signal corresponding to the acetylcholine concentration. 

The instability of fc(NH2)2 towards oxidation is certainly the reason that it cannot be used as a building-block for the synthesis of ferrocene-containing polymers [72]. l,T-Di(isocyano)ferrocene, fc(NC)2, has not been described so far. 

Except for the structure containing 100% of ferrocene unit, which decomposed before melting, all the organometallic copolymers exhibited birefringent melts. Nematic textures were identified by means of polarized optical microscopy and, in one case, by X-ray diffraction studies. For comparison purposes, a polymer without ferrocene unit was prepared, but showed no mesomorphism. The authors deduced that the ferrocene framework was contributing to the liquid crystallinity of the ferrocene-containing polymers. 

Ferrocene-containing polymers 27 and 28 were soluble in dichloromethane and chloroform, and partly soluble in THF. Analysis by gel permeation chromatography (GPC) indicated molecular weights in the range 10000 — 20000, and revealed, therefore, an oligomeric nature for 27 and 28. 

Ferrocene has been reported to be very effective as a soot reducing agent in combustion [42 — 44]. Thus, when ferrocene compounds are incorporated in a fire retardant polymer, such as a phenolphthalein-based polymer and poly(phosphate ester)s, they have shown added advantages in that they promote extinction and reduce smoke formation by accelerated char reduction [45, 46]. The synthesis of such ferrocene-containing poly(phosphate ester)s was achieved by interfacial polycondensation using a phase transfer catalyst [47]. Accordingly, l,l -bis(p-hydroxy-phenylamido)ferrocene and l,l -bis(p-hydroxyphenylcarbonyl)ferrocene underwent condensation with various aryl phosphoroic acid dichlorides to yield two series of ferrocene-containing polymers, i.e., poly (amide-phosphate ester)s 38a and poly(ester-phosphate ester)s 38b respectively, as shown in Scheme 10-17. 

Another cooperative effort arose between Samuel McManus of the University of Alabama in Huntsville and our group. This cooperation produced results in pure heterocyclic organic chemistry, oxazoline polymerizations,96 and siloxane polymers.97 Oxysilane ferrocene-containing polymers were explored.98,99 Several bis(dimethylamino)silanes were made and reacted with 1,1 -bis(hydroxymethyl)ferrocene to give the early ferrocene oxysilane polymers 69 and 70 (Scheme 1.12).98... 

C. U. Pittman, Jr., B. Surynarayanan, Y. Sasaki, Mixed Valence, Semiconducting Ferrocene-Containing Polymers, in Advances in Chemistry Series, Number 150 Inorganic Compounds with Unusual Properties, R. B. King, Ed., pp. 46-55, ACS Publishers, Washington DC, 1976. 

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