Free‐radical polymerization of vinylferrocene. I. Kinetics

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Abstract
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.

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