UTILITY OF PULSED-FIELD GRADIENT HMBC INDIRECT DETECTION NMR EXPERIMENTS FOR POLYMER STRUCTURE DETERMINATION

The utility of pulsed-field gradient (PFG)-heteronuclear multiple bond correlation (HMBC) 2D NMR experiments for characterizing polymer structure is demonstrated. Heteronuclear multiple quantum coherence (HMQC) and HMBC indirect detection experiments provide correlations indicating the presence of one-bond and two- or three-bond connectivities, respectively; this information is vital for polymer structure determination. When HMBC methods are combined with PFG techniques artifacts are eliminated which normally limit the utility of HMBC. The elimination of these artifacts lowers the detection limit by almost two orders of magnitude, making it feasible to detect signals from the small number of repeat units bonded to defect structures, chain ends, branch points and block junctions, despite the presence of much larger resonances from the main-chain repeat units. Spectra of poly(isobutylene-b-butadiene) diblocks and poly(isoprene-b-styrene) diblocks are used to illustrate these advantages.