New 3D NMR Pulse Sequences for Characterization of Polymer Chain End Structures

Abstract

A series of three-dimensional (3D) nuclear magnetic resonance (NMR) pulse sequences, utilizing pulsed-field gradients (PFG) techniques, were developed or adapted from biological experiments for applications in the characterization of the structures of polymers and other heteroatom-containing organic materials, in much the same way that the data from multiple 3D NMR experiments have been used in biological structure determination. This initial Communication describes variations of an1H/X/Y chemical shift correlation (HXY) experiment, and an HCX sequence (Y =13C) is combined with13C homonuclear isotropic mixing to generate new pulse sequences which provide additional structural information. Spectra of polystyrene and poly(α,β-13C2-styrene) (PS) prepared by diphenylphosphinyl radical (DPPR) initiated polymerization of α,β-13C2-styrene are used to illustrate the application of these techniques for characterization of polymer chain end structures. While polymers are used to illustrate the applications of these pulse sequences, they can just as easily be used to study other organic structures containing an NMR-active X nucleus. Organometallic chemistry is especially suited for applications of these NMR experiments.