C-13-NMR SPECTROSCOPY OF POLY(BETA-SUBSTITUTED BETA-PROPIOLACTONE)S - TACTICITY RECOGNITION IN 1,5-SUBSTITUTED POLYMER SYSTEM AND STEREOSPECIFIC CONTACT OF SHIFT-REAGENT

13C-NMR spectroscopy has been found to be effective for observing the dyad tacticity in poly(β-substituted β-propiolactone)s, a 1, 5-substituted polymer system which had been difficult to investigate by 1H-NMR spectroscopy. Although the dyad resonances have very similar chemical shifts, 13C-NMR spectroscopy provides a useful diagnosis for polymer stereoregularity. Addition of a shift reagent, Eu(DPM)3, is helpful for the polymers whose tacticity separation in the 13C NMR is insufficient. The lanthanide-induced shift occurs stereospecifically, resulting in a stronger low-field shift for meso-dyad signals than for racemic dyad signals. The stereospecificity may be caused by small differences in the pseudocontact angle xi of the Eu ion with the meso and racemic-dyad units in the polymer chain. In the poly-β-esters the carbon atoms sensitive to tacticity recognition include the carbonyl carbon and main chain methylene carbon atoms, whereas the methine carbon is insensitive. © 1978, American Chemical Society. All rights reserved.