Correlations between odour activity and the structural modifications of acrylates

Acrylates (acrylic esters) are versatile monomers that are widely used in polymer formulations because of their highly reactive α,β-unsaturated carboxyl structure. Commonly used acrylates such as butyl acrylate are known to emit a strong unpleasant odour, and the monomers are therefore potential off-odorants in acrylic polymers. However, up to now, the odour properties of structurally related acrylic esters have not been characterised in detail. To obtain deeper insights into the smell properties of different acrylates, we investigated the relationship between the molecular structure and odour thresholds as well as the odour qualities of 20 acrylic esters, nine of these synthesised here for the first time. The OT values of 16 acrylates fell within the range from 0.73 to 20 ng/L_air, corresponding to a high-odour activity. Moreover, sec-butyl acrylate and 2-methoxyphenyl acrylate showed even lower OT values of 0.073 and 0.068, respectively. On the other hand, the OT values of the hydroxylated acrylates 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate were 5-244 times higher than those of the other compounds, demonstrating that the presence of a hydroxyl group obviously favours odour inactivity.