CHARACTERIZATION OF POLYMERIC MATERIALS BY SOLID STATE CARBON-13 NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY (NMR, POLYETHYLENE, POLYOXYMETHYLENE, POLYURETHANE, UREA-FORMALDEHYDE, EPOXY RESINS).

摘要

Recent developments in nuclear magnetic resonance (NMR) spectroscopy e.g., cross-polarization (CP) between dilute carbon spins and abundant proton spins, magic angle sample spinning (MAS) and high power dipolar decoupling have made it possible to study a wide variety of polymeric solids such as insoluble networks, semicrystalline polymers, segmented block copolymers and others. These basic techniques are discussed from both theoretical and experimental view points for carbon-13 nuclei. Applications of solid state magic angle C-13 NMR techniques have occurred in the following areas of polymer science: (a) polymer morphology, (b) polymer conformation, (c) polymer chain dynamics, and (d) polymer chemistry. In order to gain additional information in these areas, we have used a series of various NMR pulse sequences along with line narrowing techniques. We have studied insoluble polymers such as epoxy resins, urea-formaldehyde resins, and gamma-irradiated high density polyethylene. In these polymers, the chemical shift of the C-13 NMR peaks and their intensities are sensitive to structural differences arising from variations in the experimental conditions of the polymer sample preparations. Weak resonances arising from the effect of high energy radiation on the high density polyethylene are detected including resonances from cross-link points. Magic angle solid state NMR pulse sequences are used to isolate amorphous resonance from the crystalline resonance and relate their chemical shift to chain conformations. Polyethylene, polyoxymethylene, poly(ethylene terephthalate), and polyurethanes were studied. Multicomponent behavior in their relaxations is observed on the basis of the C13-H1 dipolar interactions and spatial inhomogeneities. Other applications include the determination of non-phase segregated molecules in block copolymers of polyurethanes.