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

Abstract

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 ¹H NMR spectrum of VAE samples were assigned as follows: 2.01 ppm for CH₃ of oxyacetyl groups, 1.5-1.8 ppm for the backbone CH₂ connected to vinyl alcohol or oxyacetyl groups, and 1.2 ppm for the backbone CH₂. Based on these assignments, an ¹H 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 ¹H NMR internal standard-based quantification method. For the vinyl acetate monomer that was tested as a proxy for the oxyacetyl group, the ¹H 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 ¹³C 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 ¹H NMR internal standard-based quantification method was established for the determination of the main components of VAE-type adhesives/emulsions.