NMR Methods for Solid Polymers

Abstract

The materials properties of solid polymers are governed only in part by their molecular structure, which can be controlled by carefully designed chemical synthesis. They also strongly depend on the organization of the macromolecules in the solid state, e.g. the phase behavior, morphology, molecular order, and molecular dynamics. These macroscopic and molec­ ular parameters are influenced by the processing that follows the chemical synthesis. In order to understand structure-property relationships in poly­ mers for improvement and optimization of their behavior, experimental techniques are needed that can probe microscopic and molecular param­ eters in the solid state. The rapid methodical development of solid state nuclear magnetic resonance (NMR) has opened up new possibilities in this area. The most important advantage of NMR is its selectivity, which can be achieved in two ways. One route is high resolution NMR in solids, in particular of 13C in natural abundance. The improved resolution together with an enhance­ ment of signal intensity is achieved by a combination of I H/l3C Cross Polarization, high power proton decoupling and Magic Angle Spinning (CPMAS-NMR). This technique is now standard, and its methodology as well as numerous applications to solid polymers have already been reviewed (1-10). The structural information obtained from such 13C-NMR spectra is similar to that obtained from liquid state NMR spectroscopy. There, the isotropic chemical shift is an indicator of the structural element to which the detected nucleus belongs and of the conformation of the molecule. In addition, line shape and spin relaxation can be exploited to