1H NMR and 13C NMR investigations of sequence distribution and tacticity in poly(vinyl alcohol-co-vinyl levulinate)

The microstructure of poly(vinyl alcohol-co-vinyl levulinate) (VOH-VLA copolymer) was studied by H-1 NMR and C-13 NMR techniques. The sequence distributions could be obtained from the six methine triads observed in the 500-MHz 1H NMR spectra of the copolymers: the three methylene dyads and the three carbonyl triads observed in 125.6-MHz C-13 NMR spectra of the copolymers. The reaction activity order of different tacticity hydroxyl in PVA was found to be rr > mr > turn by investigating VOH-centered methine tacticity triads. The vinyl levulinate content (VLC), the number-average sequence length, dyad-triad relation and triad-triad relation (R) were calculated from methine triads, methylene dyads and carbonyl triads in 1H NMR and C-13 NMR spectra successfully, and they were in good agreement with each other. The consistency of the dyad-triad and triad-triad relations shows that head to head or tail to tail fragments are hardly present in VOH-VLA copolymer. (c) 2006 Elsevier Ltd. All rights reserved.