Nuclear magnetic resonance molecular microstructure

Since about 1960 nuclear magnetic resonance (NMR) spectroscopy has become an important tool for the study of chain configuration, sequence distribution and microstructure of polymers. Its use started from early broad-line studies of the one-set of molecular motion in solid polymers and passed through the solution studies of proton NMR, to the application of the more difficult but more powerful carbon-13 NMR methods to both liquids and solids. 

Carbon-13 nuclear magnetic resonance has become an in ortant tool with which to study the microstructure and molecular dynamics... 

In earlier literature reports, x-ray data of a-based ceramics, the /3-like phase observed in certain silica minerals was explained by a structural model based on disordered Q -tridymite. However, others have suggested that the structure of the stabilized jS-cristobalite-like ceramics is closer to that of a-cristobalite than that of Q -tridymite, based on the 29Si nuclear magnetic resonance (NMR) chemical shifts (Perrota et al 1989). Therefore, in the absence of ED data it is impossible to determine the microstructure of the stabilized jS-cristobalite-like phase. ED and HRTEM have provided details of the ceramic microstructure and NMR has provided information about the environments of silicon atoms in the structure. Infrared spectroscopy views the structure on a molecular level. 

If you have been working your way through this epic in a more or less linear fashion, then you might have started to ask yourself some fundamental questions such as, How do you know if a vinyl polymer is isotactic, or atactic, or whatever How do you know the composition and sequence distribution of monomers in a copolymer How do you know the molecular weight distribution of a sample This last question will have to wait until we discuss solution properties, but now is a good point to discuss the determination of chain microstructure by spectroscopic methods. The techniques we will discuss, infrared and nuclear magnetic resonance spectroscopy, can do a lot more than probe microstructure, but that would be another book and here we will focus on the basics. 

Spectroscopic techniques, in general, are very well suited for investigation into molecular aspects such as local molecular arrangements, molecular dynamics, and molecular interactions. However, for many microemulsions, in particular those that simultaneously contain large amounts of water and oil, these aspects are rather uninteresting. Local molecular dynamics are determined by short-range interactions and are essentially independent of the self-assembly structure. Nuclear magnetic resonance (NMR) is, however, particular as a spectroscopic technique in that it can also provide information on other central matters such as phase behavior and microstructure. In particular, NMR self-diffusion and, to some... 

IR spectroscopy is the most widely-used method for characterizing the molecular structures of polymers, principally because it provides a lot of information and is relatively inexpensive and easy to perform. However, it is not simple to interpret absolutely the more subtle features of IR spectra, such as those due to differences in tacticity. Such interpretations are usually made on the basis of information obtained from other techniques, in particular nuclear magnetic resonance spectroscopy which is by far the most powerful method for determining the detailed molecular microstructures of polymers. 

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