Mossbauer studies of polyvinylferrocenes.

Polymers of vinylferrocene and 1,1'-divinylferrocene have been investigated using Fe 57 Mossbauer spectroscopy and other spectroscopic techniques. In studies of the radical polymerisation of vinylferrocene the novel FeIII species, previously proposed as the product of monomolecular termination of the reaction could not be observed. Polymerisation of vinylferrocene in chloroform occurred only in oxygen-free conditions, as previously reported, but the kinetics of the polymerisation were found to be very sensitive to impurities. 13 C n.m.r. studies of polyvinylferrocene have given results which contradict previously published work and correct peak assignments have now been made. The structures of polymers from 1,1'-divinylferrocene have been investigated by techniques that had not previously been used. Previous workers had concluded that the polymers produced by both radical and cationic initiation contained three carbon bridged ferrocene units. However, the Fe 57 Mossbauer spectra revealed significant differences between the polymer structures. The quadrupole splitting (Q.S.) for polymers from cationic initiation = 2.39(2) mm s-1 with Q.S. for polymers from radical initiation = 2.29(2) mm s-1. This and other spectroscopic evidence supports a cyclopolymer structure for the polymers produced by radical initiation, with cationic initiation yielding polymers by an intermolecular polyaddition mechanism. The structures proposed have been confirmed by the synthesis of and spectroscopic comparisons with relevant model compounds. A polymer from anionic initiation of 1,1'-divinylferrocene previously unreported, has been prepared and shown to contain a trimethylene bridge, identical to that of the radically-initiated polydivinylferrocene.Variable temperature Fe 57 Mossbauer studies have been carried out on ferrocene and on polymers of vinylferrocene and 1,1'-divinylferrocene produced via anionic and cationic initiation. The treatment of the temperature dependence of the Mossbauer absorber recoiless fraction for crystalline solids has been extended to describe the vibrational properties of these amorphous polymers. An unusual nonlinear dependence of InA with temperature has been observed for the polymeric materials. The observed behaviour could not be explained on the basis of a modified Debye model for amorphous materials, even when intramolecular vibrations were included. However, a good fit to the experimental data was obtained with physically significant fitting parameters when it was assumed that each macromolecule vibrated within an anharmonic potential.