Triple resonance Polymer characterization

In this work the applications of three dimensional (3D) solution NMR techniques for characterizing the structures of synthetic polymers and dendrimers are illustrated, including the characterization of polymer chain-end structure, monomer sequence, stereosequence, and branching. The utility of triple resonance and pulsed field gradient NMR techniques in these research endeavors are discussed. 

NMR has been a powerful technique for structural analyses of macromolecules. However, ID NMR spectra of PDMS are usually complicated due to signal overly. Their complete characterization often requires combinations of several techniques. Multidimensional NMR techniques, especially inversely detected 3D heteronuclear shift correlation experiments, offer the opportunity to obtain the complete structural characterization by using NMR experiments alone. Biological 3D-NMR experiments are usually performed in conjunction with uniform and isotopic labeling. In polymer chemistry, when isotopic labeling is possible, it is often very difficult and expensive. By modifying the 3D-pulse sequence used for biopolymers, triple resonance 3D-NMR techniques have been adapted for sbufying the structures of polymers, which involve H- C- P, H- C- Si spin... 

Triple resonance 3D-NMR experiments can be useful for studying polymeric structures without resorting to isotopic labeling, even when the nuclei involved are present in low natural abundance. This study of MD3M shows that the considerable spectral dispersion obtained in the Si NMR spectra of siloxanes, compared with the narrow H and C chemical shift ranges, permits detailed examination of the structure of PDMS by the 3D H/ C/ Si NMR correlation experiment. These techniques can also be usefiil for characterizing star-branched polymers which contain NMR active nuclei, polymers with low concentrations of heteroatoms (e.g. at the chain end or at low occurrence branch points) and many organometallic compounds. 

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