The Microstructures and Molecular Interactions in Multiphase Polymers: Insights from Solid-State NMR Spectroscopy

In recent decades, solid-state nuclear magnetic resonance (NMR) spectroscopy has been playing an important role in the characterization of polymer materials. To some degree, it has become one of the indispensable tools for studying the microstructures, segmental dynamics and inter-/intra-molecular interactions and elucidating the structure-functionality-property relationship of multiphase polymer materials, because the anisotropic spin interactions in the molecules can be selectively manipulated via various radiofrequency pulse sequence design. As a result, NMR can provide important information on a length scale from 0.1 nm to 100 nm and a time scale from 1 ns to 100 s. Herein, in this current review article, we will review some of our recently developed solid-state NMR approaches specifically for applications in polymers, including quantitative determination of compositional contents, characterization of crosslinking/entanglement density and inhomogeneity of the network, hydrogen bonding interactions between segments, and so on. A variety of typical examples, including self-healing supramolecular rubbers, thermal reversible polyurethanes, dual-cross-linked hydrogels, elastomers, etc., are given in detail, showing how various solid-state NMR approaches were implemented to quantitatively characterizing the structures, molecular interactions, and crosslinking network. Furthermore, due to the presence of heterogeneous dynamic in multiphase polymers, the applications of traditional solid-state NMR techniques are sustainably limited, and we also developed corresponding novel solid-state NMR approaches to overcome the limitations and enhance the spectral resolution and signal sensitivity.