Improved NMR characterization of high‐molecular‐weight polymers and polyelectrolytes through the use of preliminary ultrasonic degradation

High‐molecular‐weight polymers, especially ionic polymers, give rise to highly viscous solutions which are likely to entrap air bubbles, even at low concentrations. The 13 C NMR spectra of these solutions exhibit poor signal‐to‐noise ratios and broad bands due to the shortened T 2 relaxation times. Qualitative evaluation is thus made very difficult, and quantitative evaluation becomes impossible. In 1 H spectroscopic analysis of xanthan, these problems occur at concentrations as low as 0,5 wt.‐%. A method of viscosity reduction is required that reduces the molecular weight but does not affect the tacticity or comonomer distribution nor lead to the formation of monomers. From the various methods that were examined, ultrasonic degradation was found to be the best means of fulfilling these requirements. This study includes both coiled synthetic polymers, such as polyacrylamide or poly(acrylamide‐ co ‐sodium acrylate), and semirigid biopolymers, such as xanthan or schizophyllan, with a view to finding a generally applicable method. It was shown that the recording time could easily be reduced by a factor of up to 20 and that the resolution was enhanced. No change in the functional groups was observed in any of the polymers, and in the case of xanthan no cleavage of side chains occurred. In schizophyllan the triple helix structure also remained intact after degradation. It is postulated that degradation is attributed to elongational flow conditions produced by cavitation in ultrasonic fields.