Synthesis and Sequence Analysis of Highly Blocky Acetylated Poly(vinyl alcohol) Copolymers

Sequence distribution in poly(vinyl alcohol) (PVOH)-based copolymers strongly influences their properties, yet methods for producing and characterizing highly blocky microstructures remain limited. Conventional postpolymerization hydrolysis and reacetylation methods yield only moderately blocky microstructures, limiting access to well-defined copolymer sequences. To access highly blocky acetylated poly(vinyl alcohol) (AcPVOH) microstructures, PVOH was acetylated in the heterogeneous (i.e., semicrystalline), supercritical CO2-swollen film state. A matched set of random rAcPVOH and blocky bAcPVOH copolymers with degrees of acetylation spanning 3–30% were prepared, and differences between their 1H and 13C NMR spectra were explored. Dyad peak assignments were confirmed using HSQC and HMBC spectroscopy. The copolymer blockiness was quantified using 13C NMR spectroscopy, where the random copolymers exhibited blocky character η values close to 1, consistent with statistically random sequencing. In contrast, the blocky products had η values around 0.25, indicating they were significantly blockier than any previously reported blocky AcPVOH copolymer. Blockiness was also quantified using the randomness factor R, where the blocky products exhibited R values well above 80, consistent with a highly blocky microstructure. Together, these results establish scCO2 acetylation as a robust route to synthesizing highly blocky PVOH-based copolymers and lay the fundamental groundwork for elucidating the microstructure of these commercially relevant water-soluble polymers using NMR spectroscopy.