Alkyl groups, ferrocene polymers

The presence of at least one alkyl group on the cyclopentadienyl motif is required to induce solubility in these poly(ferrocenylene persulfide)s. These polymers show two reversible oxidations. This type of electrochemical behavior is fairly common in ferrocene polymers where the ferrocene units are separated by short spacers as will be pointed out in the next section. 

Chemical oxidants also allowed switchable hydrogel formation by reversible competitive hosting of low molecular mass ferrocene units within cyclodextrins. Here, cyclodextrin complexes the otherwise-associating alkyl side chains, which reduces the viscosity of this well-formulated mixture. However, the alkyl groups start to associate under gel formation when reduced ferrocenecarboxyUc acid is added. Then, ferrocene interacts preferentially with the cyclodextrin. This state can be reversed upon chemical oxidation due to the unfavorable inclusion complexation of ferrocenium units with cyclodextrin [254]. Based on similar mechanisms, a redox-dependent shape memory polymer has been generated [340] and also the adhesion of different gels can be switched [341]. 

Polyphosphazenes with simple alkyl and aryl substituents directly attached to the backbone by P-C linkages can be prepared by the condensation polymerization of N-silylphosphoranimine precursors. These simple polymers can then be converted to a variety of functionalized polyphosphazenes by derivatization reactions. In this paper, the synthesis and characterization of some derivatives of poly(methylphenyl-phosphazene), [Me(Ph)P=N]and the copolymer, [Me(Ph)P=N]j [Me2P=N)y, are discussed. These polymers include grafted copolymers, water soluble carboxylated polymers, and polymers with silyl, vinyl, alcohol, ester, ferrocene, phosphine, thiophene, and/or fluoroalkyl groups. 

A number of ferrocene-based polymers containing other metals or metalloids in their structures have been examined. Carraher and Lessek reported that tin-containing polyesters of ferrocene (112) could be prepared by reaction of the organ-otin dihalides (110) with disodium ferrocene dicarboxylate (111) as shown in Scheme 28. The polymerization reactions proceeded rapidly, with yields reaching maximum values between 30 s and 2 min. Polymer yields increased with smaller alkyl substituents and with the phenyl substituent, and yields also increased by changing the leaving group from Cl to Br to I. All of these polymers were foimd to be insoluble in the solvents tested. 

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