Complex esters are an important class of compounds in the personal care market. These include fatty derivatives of neopentyl glycol (NPG), trimethylol propane (TMP) and pentaerythritol (PE). Their structures are given in Figure 1, Figure 2 and Figure 3, respectively. These materials are made from mono-substituted fatty acids and di-, tri- or tetra-functional hydroxyl compounds. They are not polyesters.
Polyesters are made with multifunctional acids and hydroxyl compounds. They offer the cosmetic formulator the potential to make products with a wide range of cushion and playtime. This, in turn, results in many cosmetically elegant formulations.
One of the major uses of complex esters is for low viscosity, cosmetically elegant oil phases. The PE esters have the most cushion and playtime while the NPG has the least cushion and is a dry oil.
The low viscosity is obtained using branched, monounsaturated or iso fatty acids. Table 1, Table 2, Table 3 and Table 4 compare oleate esters, eructate esters, C-20 guerbet acid esters and isostearate esters.
The guerbet C-20 esters have the lowest iodine value, meaning they have the best oxidative stability. Iodine value increases in the following order: guerbet C-20 esters, isostearate esters and euruic esters and oleate esters are about equal. Fragrance interactions also need to be considered when using esters with high iodine values.