Development of an NMR-based quantification method for the main components in VAE-type adhesives/emulsions.

It is important to accurately test the content of the main components (i.e., oxyacetyl, vinyl, and vinyl alcohol) of VAE-type adhesives/emulsions. In this study, we first investigated the solubility of dried VAE samples. Dimethyl sulfoxide (DMSO) was the best solvent tested, and at a sample concentration of 10,000 µg/mL, complete dissolution was achieved after 3 h of ultrasonication. Second, different chemical shifts of protons in the H NMR spectrum of VAE samples were assigned as follows: 2.01 ppm for CH of oxyacetyl groups, 1.5-1.8 ppm for the backbone CH connected to vinyl alcohol or oxyacetyl groups, and 1.2 ppm for the backbone CH. Based on these assignments, an H NMR normalization-based quantification method was established. Meanwhile, correction factors of each VAE functional group relative to the internal standard benzyl benzoate were calculated to establish an H NMR internal standard-based quantification method. For the vinyl acetate monomer that was tested as a proxy for the oxyacetyl group, the H NMR internal standard-based quantification method yielded a closer result (37.44%) to the classical method (37.30%) than the normalization-based method. The method exhibited good repeatability and reproducibility (repeatability RSD < 5%, reproducibility RSD: vinyl and oxyacetyl < 5%, vinyl alcohol < 11.24%). In contrast, a C NMR internal standard-based quantification method was deemed unsuitable for the quantitative analysis of VAE main components due to its high sample concentration requirements, lengthy test durations, and tendency to underestimate the actual contents. Finally, a H NMR internal standard-based quantification method was established for the determination of the main components of VAE-type adhesives/emulsions.