Quantitative 2D HSQC NMR determination of polymer structures by selecting suitable internal standard references

A new analytical method based on the 2D HSQC NMR sequence is presented, which can be applied for quantitative structural determination of complicated polymers. The influence of T-1 and T-2 relaxations, off-resonance effects, coupling constants and homonuclear couplings are discussed. It was found that the T-2 values measured on polymeric samples with the conventional HSQC-CPMG sequence could not be used to correct the errors caused by T-2 relaxations during the polarization transfer delay. A unique way of selecting the proper internal standard reference signal(s) is therefore proposed to eliminate the major errors caused by T-2 relaxations, resonance offsets, coupling constant deviations and homonuclear couplings. Two polymer samples, a cellulose triacetate and an acetylated lignin, have been used to illustrate the principles. The methodology developed in this work is robust to instrument miss-setting and it can find wide-spread applications in areas where a quantitative analysis of structurally complicated polymers is necessary. Copyright (C) 2006 John Wiley & Sons, Ltd.