Structure and segmental motions in symmetrically substituted poly(ferrocenylsilanes): A carbon-13 CPMAS NMR contact time study

The structure and thermal behavior of two organometallic polymers, poly(ferrocenyl dimethylsilane) (I) and poly(ferrocenyl di-n-butylsilane) (II), have been examined using a variety of physical characterization methods which reveal differences in their crystalline structures and associated segmental librations. In addition to examination with differential scanning calorimetry and wide-angle X-ray scattering, solid-state C-13 NMR spectra were acquired for a wide range of H-1-C-13 contact times. The spectra of I at room temperature exhibit two isotropic chemical shifts for the methyl groups, indicating the presence of different environments. The initial cross-polarization (CP) times of crystalline, protonated carbons are interpreted with reference to values found in the literature. The main chains of both polymers were found to be fairly rigid on the time scale of T-CH, but the side chains of II are very disordered. The relevance of the C-13 measurements at room temperature is discussed with regard to a higher temperature transition indicated in the DSC trace of II.