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

✍ Scribed by Takeshi Saito; Peter L. Rinaldi

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 145 KB
• Volume: 130
• Category: Article
• ISSN: 1090-7807
• DOI: 10.1006/jmre.1997.1290

✦ Synopsis

A series of three-dimensional (3D) nuclear magnetic resonance long-range J CP or performing 13 C-13 C relay-type experi-(NMR) pulse sequences, utilizing pulsed-field gradients (PFG) ments when 13 C is present at natural abundance are extremely techniques, were developed or adapted from biological experidifficult because of the low chain end concentrations and ments for applications in the characterization of the structures of efficient relaxation which broadens the resonances. Therepolymers and other heteroatom-containing organic materials, in fore, a,b-13 C 2 -styrene was polymerized by initiation with much the same way that the data from multiple 3D NMR experi-DPPR to aid in the identification of resonances from the ments have been used in biological structure determination. This structure fragments formed by the addition of the first two initial Communication describes variations of an 1 H/X/Y chemical monomer units in the polymerization. shift correlation (HXY) experiment, and an HCX sequence (Y Å One of the most probable structures formed at the poly-13 C) is combined with 13 C homonuclear isotropic mixing to gener-(a,b-13 C 2 -styrene) (PS) chain ends is ate new pulse sequences which provide additional structural information. Spectra of polystyrene and poly(a,b-13 C 2 -styrene) (PS) prepared by diphenylphosphinyl radical (DPPR) initiated polymerization of a,b-13 C 2 -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 which results from an initiation step that involves addition of these NMR experiments.