The complicated chemical structure of poly(vinyl butyral) (PVB) as well as its acetalization mechanism was unveiled by multidimensional NMR with the assistance of the 13 C labeling. The isotope enrichment significantly suppresses the NMR signal from the side groups, which enables us to precisely determine the sequence distribution of various monomers, i.e., vinyl butyral (VB) and vinyl alcohol (VA), along the PVB backbone. The primary, secondary, and tertiary carbons were directly identified by NMR spectral editing through 13 C distortionless enhancement by polarization transfer (DEPT) NMR experiments. Various 2D-NMR experiments, including COSY, NOESY, HMQC, and INADEQUATE, were adopted to establish homo-and heteronuclear coupling through either chemical bond or space correlation. Because only the PVB backbone is 13 C-enriched, all 1 H and 13 C NMR spectra provided unprecedented resolved information on various sequence information. In total, 13 13 C and 18 1 H resolved NMR peaks are assigned. Based on the accomplished 13 C NMR peak assignment and quantitative 13 C NMR of PVB with different acetalization degrees as well as numerical modeling, a possible acetalization reaction mechanism is proposed.

The addition of small molecular plasticizer is an efficient strategy to increase the process ability and macroscopic performance of poly(vinyl alcohol) (PVA). However, how the plasticizer influences the chain dynamics and morphology deserves further investigation. In this work, the PVA film with varying glycerol addition levels was used as the model system. The increasing glycerol addition‐level results in the depression of the melting temperature and crystallization temperature, which in line with Flory's theory. The enhanced chain dynamics in the mobile domain was accessed by low‐field NMR, whereas that in the crystalline region remains constant. The domain size as well as the morphology of the mobile phase are accessed by 1H spin‐diffusion NMR. The results indicate the increasing dimensionality of the plasticized PVA film with increasing the addition level of glycerol, where the addition level below 25 wt% leads to the dimensionality of 1D, and higher than 25 wt% results in the dimensionality of 2D. Current results elucidate the critical role of the plasticizer in modulating the dynamics heterogeneity of the plasticized polymer film, which is closely related to the macroscopic performance of the products.