Springer Ab Initio Calculations of Conformational Effects on 13C NMR Spectra of Amorphous Polymers: 35 (NMR Basic Principles and Progress, 35)

In NMR, it is well-known that the chemical shift conveys structural informa tion, e. g. a carbonyl carbon will have a resonance frequency appreciably dif ferent from a methyl carbon, etc. The relation between structure and chemical shift is mostly established by empirical rules on the basis of prior experience. It is only quite recently that the advent of both comparatively cheap comput ing power and novel quantum chemistry approaches have provided feasible routes to calculate the chemical shift at the ab initio level for molecules of reasonable size. This raises the question whether application of these novel theoretical concepts offers a means of obtaining new structural information for the complex chain molecules one deals with in polymer science. Solid state 13C-NMR spectra of glassy amorphous polymers display broad, partially structured resonance regions that reflect the underlying disorder of the polymer chains. The chemical shift responds to the variation of the ge ometry of the chain, and the broad resonance regions can be explained by an inhomogeneous superposition of various chain geometries (and thus chem ical shifts). In this review, we present a novel approach to combine polymer chain statistical models, quantum chemistry and solid state NMR to pro vide quantitative information about the local chain geometry in amorphous polymers. The statistical model yields the relative occurrence of the various geometries, and quantum chemistry (together with a force field geometry op timization) establishes the link between geometry and chemical shift. From the Back Cover The elucidation of the structure of amorphous systems is one of the most challenging problems of condensed-matter research. Our lack of knowledge about the detailed structure of disordered systems on the molecular level contrasts with the rapidly growing importance of such materials in science and technology. Solid state NMR is of key importance in this area, since it can provide detailed information about internuclear distances and torsional angles in crystals and glasses alike. Common examples of amorphous systems are glassy polymers. There, structural information is encoded in the chemical shifts of 13C-NMR spectra. This volume presents a powerful new approach to unravel this information by combining polymer statistical models, quantum chemistry and solid state NMR. It reviews the present state of the art, reports previously unpublished results, and indicates ways for further development in the future.