Chapter 25 NMR characterization of functionalized polysiloxanes

Abstract

Polysiloxanes are polymeric materials prepared by the condensation of suitably substituted silanes. Solid-state nuclear magnetic resonance (NMR) proved useful in elucidating the structures of functionalized polysiloxanes. The NMR approaches that have been employed include natural-abundance; high-resolution solid-state 13 C, 15 N, 29 Si, and 31 P NMR with cross polarization and magic-angle spinning (CP-MAS) and 1 H NMR with combined rotation and multiple-pulse spectroscopy (CRAMPS). The 13 C NMR is useful in establishing the primary structures of the pendant groups of some functionalized polysiloxanes and in confirming these structures in other cases. The results of 15 N can also play a role in establishing the presence and nature of proton transfer and/or hydrogen bonding, for example in amino-functionalized polysiloxanes. In addition, 29 Si CP-MAS NMR experiments are valuable for assessing the nature of the polysiloxane framework and the local siloxane structures in the region of the pendant group attachments. Relaxation studies, including measurement of 1 H spin-lattice relaxation times via X-detected 1 H→X cross-polarization techniques are useful for both assessing the general degree of atomic-level mobility and establishing domain-based homogeneity/heterogeneity.