NMR imaging of polymers

Chapter 7 of this text details the use of NMR imaging methods to determine structure and function of crosslinked rubbers. In this section we review the NMR imaging of rubbers swollen with small molecules. Two sets of experiments are described, namely the study of diffusion of small molecules into a previously unswollen rubber (macroscopic diffusion), and the measurement of images of the solvent and/or polymer after equilibrium has been achieved. 

NMR studies of polymers, and magnetic resonance imaging (MRI). In an interesting study, the solid state CPMAS NMR data sets for a pharmaceutical compound were analyzed using DECRA. In these experiments the exponential decay of the signal intensity in the data matrix D decayed as a result of H spin lattice T relaxation. The DECRA results allowed the resolution of two distinct crystalline polymorphs within the compound. DECRA has also used to analyze the C MAS NMR spectra of irradiated cross-linked polyolefin cable insulation. In this study, the two proportional data... 

These examples demonstrate the principal feasibility of imaging rigid polymers while addressing questions of general interest. Yet the experimental efforts involved are substantial and the samples need to be kept small. Therefore, NMR imaging of rigid solids appears to be restricted to selected fundamental investigations. 

Many methods for improvements of the spatial resolution in NMR imaging of solid materials have been proposed with different impact on applications in polymer science [8, 9, 11-13, 21]. For the great variety of techniques only those are reviewed in Sections 5.1.3 and 5.1.4 below, which are being applied successfully to problems in polymer science. Depending on the dominating features, the techniques can be classified into frequency and phase encoding approaches. 

Applications of NMR imaging outside the medical field have been published in a variety of books and journals [8-13, 21, 86, 108-115]. A rather important subject for applications of NMR imaging is polymer science, as polymers are rich in protons, the most sensitive, stable NMR nucleus, and many polymer materials are often soft, so that the homonuclear dipole-dipole interaetion among protons is partially averaged by molecular motion. Thus, polymers are far more suitable to NMR imaging than for instance ceramic materials. 

---