The polymerization of vinylferrocene in benzene at 60°C in the presence of 2,2′‐azobisisobutyronitrile has been studied. Densities and apparent densities were determined and rates of polymerization measured dilatometrically. The results show that vinylferrocene does not obey normal vinyl polymerization kinetics. Thus the rate of polymerization is proportional to the mean monomer and mean initiator concentrations both raised to a power of 1.1, and the degree of polymerization is independent of the initiator concentration. The polymerization reaction also has a high overall activation energy of 139 kJ/mole. The unusual kinetics are due to a monomolecular termination of the polyvinylferrocene chain radical which is also intermolecular with respect to the chain radical. Termination occurs by an intramolecular electron transfer reaction from a ferrocene nucleus to the growing chain radical which deactivates the chain radical and produces a polymer molecule containing a high spin Fe (III) complex. The presence of this species has been confirmed by Möussbauer and ESR spectroscopy. The rate constant for termination is between 3 and 60 sec‐1. Intramolecular electron transfer has not been previously observed in vinyl polymerizations. The term “intralectran” is suggested to describe this new type of termination. Vinylferrocene readily undergoes transfer to monomer (with a transfer constant equal to about 8 × 10‐3) and to polymer, but not to benzene.

The spectroscopic and physical properties of poly(vinylferrocene) prepared by free‐radical polymerization in benzene are discussed. The results obtained in these studies are in accord with the kinetic analysis of the polymerization reactions in benzene. ESR spectroscopy shows that the polymer is paramagnetic and contains a species which is identified by Mössbauer spectroscopy as an ionically bound complex of Fe(III) in a high spin (3d5) configuration. The concentration of this species is shown to be dependent upon kinetic parameters. Magnetic susceptibility measurements show that the polymer does not contain any oxidized ferromagnetic impurities. Infrared spectroscopy indicates that the polymer contains vinylidene groups. The presence of these groups is explained by chain transfer to monomer followed by reinitiation. Ultraviolet spectroscopy also suggests the presence of unsaturation in the polymer. Gel‐permeation chromatography indicates that poly(vinylferrocene) is branched even at low conversions. The effect of transfer reactions and the intramolecular electron transfer termination of the chain radical on the structure of poly(vinylferrocene) is discussed. The glass transition temperature and thermal stability of the polymer are also examined.

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Organic boron polymers are of interest to AWE, and a significant improvement would be to make components from a single phase material that enables the boron content to be maximised and the elastomeric properties to be tuned to requirement. This paper is a summary of the work carried out towards the synthesis and characterisation of poly(m‐carborane‐siloxane) rubbers. These rubbers have been synthesised by the Ferric Chloride‐catalysed condensation reaction between dimethoxy‐m‐carborane terminated monomer and dichlorodimethylsilane. Phenyl modified and Phenyl‐vinyl modified variations have been synthesised in addition to the unmodified poly(m‐carborane‐siloxane) polymers. The unmodified poly(m‐carborane‐siloxane) shows some crystallinity but the modified versions are amorphous and have good elastomeric properties. Overall, the measured boron content is in close agreement to that expected from the repeat unit, suggesting the synthesised rubbers have been successfully prepared. It is also demonstrated that the carborane unit offers increased thermal stability and retention of ‘rubber‐like’ properties even after ageing at high temperature.

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