Molecular ring rotation in poly(vinylferrocene)

Abstract

We investigate the ring rotation dynamics in poly(vinylferrocene) (PVFc) using incoherent neutron spectroscopy. PVFc contains ferrocene units laterally attached to a polymer backbone, allowing for one cyclopentadienyl ring of the organometallic sandwich structure of ferrocene to undergo rotational jump diffusion. The barrier of rotation is found to be broadly distributed, but the dynamics can be well described using a rotation rate distribution model which is well known from the description of methyl group rotation in glassy polymers. As necessary information for the analysis of quasielastic scattering data, we measure the static structure factor of the polymer using polarized neutron diffraction. Neutron time-of-flight and backscattering data are then combined and consistently modeled over the large temperature range from 80 K to 350 K yielding an Arrhenius behavior of the jump rate distribution. The mean value of potential barrier distribution is found to be 〈E_A〉 = 9.61(2) kJ mol⁻¹ with a root mean square width of σ_E = 3.12(1) kJ mol⁻¹, being the result of superposition of constant intramolecular and heterogeneous intermolecular rotational barriers.