Magic-angle spinning polymers

Keywords multiphase polymer materials, solid-state NMR, structure characterization, morphology, conformation, cross-polarization, magic-angle spinning, polymer dynamics, chemical shift, relaxation times... 

Lindberg, J. J. and Hortling, B. Cross Polarization — Magic Angle Spinning NMR Studies of Carbohydrates and Aromatic Polymers. Vol. 66, pp. 1—22. 

Cross Polarization — Magic Angle Spinning NMR Studies of Carbohydrates and Aromatic Polymers... 

PPy was the first conducting polymer to be structurally analyzed. The discovery that a,a -disubstituted pyrroles did not electropolymerize led to the conclusion that the pyrrole units in PPy are a-linked Magic angle spinning C-NMR... 

We used modifications of the standard solid-state CP-MAS (cross-polarisation, magic-angle spinning) experiment to allow the proton relaxation characteristics to be measured for each peak in the C spectrum. It is known that highly mobile, hydrated polymers can not be seen using either usual CP-MAS C spectrum or solution NMR (6). We found, however, that by a combination of a long-contact experiment and a delayed-contact experiment we could reconstruct a C spectrum of the cell-wall components that are normally too mobile to be visible. With these techniques we were able to determine the mobility of pectins and their approximate spatial location in comparison to cellulose. 

Azo-bis-isobutyronitrile average polymer chain concentration 4-aminotoluene (p-toluidine) Brunauer-Emmet-Teller cross-linking degree Cross Polarization-Magic Angle Spinning Nuclear Magnetic Spectroscopy Cyclic voltammetry N, A-dimethylformamide... 

It was reasoned that the polymer must consist of a, a -coupled pyrrole units, with fi coupling less important, because of the fact that oc-substituted pyrroles do not polymerise whereas -substituted species do, and on the basis of magic angle spinning 13C nmr and IR techniques. The method of labelling the monomer ring positions is also shown in Scheme 3.9. 

The methods of high power decoupling, cross-polarization and magic angle spinning produce useful spectra from intractable polymers. In a rather rigid material... 

The experimental design was to study both the carbon-13 and proton relaxation as a function of temperature for both polymer and solvent, and to extend these to as high a polymer concentration as the available equipment permitted. Inasmuch as the mechanical properties of polymers can be affected considerably by small amounts of diluents, we would ultimately like to approach the bulk polymer state, where use of strong dipolar decoupling and magic angle spinning are necessary. ... 

In recent years new NMR techniques offering broad applications in stereochemical analysis have come into use. A prominent example is 2D-NMR (both 2D-resolved and 2D-correlated spectroscopy), which has been extensively applied to biopolymers (149-151). Its use with synthetic polymers has, until now, been limited to but a few cases (152, 153). A further technique, cross-polarization magic-angle spinning spectroscopy (CP-MAS NMR) will be discussed in the section on conformational analysis of solid polymers. 

During the last 15 years, the cross-polarization magic-angle spinning (CPMAS) technique (2) has been used with increasing frequency to provide detailed structural information about solid polymers and biopolymers... 

In NMR experiments, molecular mobility leads to narrowing of the resonance lines. Conversely, restricted molecular motion, as occurs in crystalline phases, causes line-broadening. Until the advent of magic angle spinning and related techniques, tliis was a hindrance to NMR studies of solid polymers. We have used it to advantage in following the orientation effects in solid PTFE. 

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