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 1H NMR and 13C 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 13C NMR spectra of the copolymers. The reaction activity order of different tacticity hydroxyl in PVA was found to be rr > mr > mm 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 13C 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.