Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate

Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is a hindered phenolic antioxidant commonly used as a polymer stabiliser.

Synthesis
Base catalysed Michael addition of methyl acrylate to 2,6-di-tert-butylphenol forms the intermediate butyl-phloretic ester. High temperature transesterification of this with stearyl alcohol gives the final product.

Applications
Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate is significantly less volatile than simpler phenolic antioxidants such as butylhydroxytoluene (BHT). This makes it more suitable to stabilising plastics, as it is not driven out by the high temperatures experienced during plastic extrusion and moulding, when they are heated to 150-320 °C (300–600 °F). It is widely used in the commodity plastics, particularly in polyethylenes and polypropylene. It has approval for use in food contact materials, such as plastic food packaging in the EU and US, amongst others.

It is one of the most common polymer antioxidants, in part because of its comparatively low price. The stearyl tail reduces volatility and gives good chemical compatibility with plastics but contributes nothing to antioxidant performance. When higher performance is needed pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate) a common alternative.