Polyesters are an important class of cosmetic ingredients. There are over 200 different types of polyesters listed in the International Cosmetic Ingredient Dictionary and Handbook with a variety of functions, including film-forming and conditioning agents for skin and hair.2 Polyesters are polymer chains comprised of repeat units linked by ester bonds as shown in Figure 1. Polyester backbones are polar due to the ester bonds and the degree of polarity is controlled by increasing/decreasing aliphatic content in the backbone and the polymer chain end groups. Generally polyesters are hydrophobic and insoluble in water but can be rendered water-dispersible or watersoluble by incorporating hydrophophilic ionizable groups into the backbone. Polyesters can be linear, branched, and/or crosslinked and the difference in the structure modulates critical physical properties such as viscosity and film formation. The polyester chemical structure can also be varied to modulate compatibility in solution and on surfaces, solubility properties, and dispersion properties. Two polyester molecules will be discussed in this paper. The primary structure of both molecules is shown in Figure 2 and the structure variations are referenced in the respective sections about this polymer. 

LexFeel™ Vibrant (Palm Acid/Adipic Acid/Pentaerythritol Crosspolymer) is a branched/crosslinked polyester according to Figure 2 with long carbon chain (C16 – C18) end groups. This specific polyester structure results in a stiff and waxy ingredient structure that can cocrystallise with waxes to provide structure and texture in cosmetic formulations. In comparison to using only traditional waxes, such as beeswax and ozokerite, addition of the LexFeel Vibrant polyester maintains structure while controlling negative effects like sweating (Fig 3). Additionally, this polyester is an amorphous and low Tg polymer compared to crystalline waxes which provides thickening of the oil phase without causing haziness or clouding. This results in an improved formulation background for pigments giving a brighter and more vibrant colour in the product and upon application. As can be seen in Figure 4, the result is higher payoff and more brilliant impactful colour upon application – ideal to deliver bold colours on trend with the colour cosmetics market. 

LexFeel 699 (Pentaerythrityl Adipate/ Caprate/Caprylate/Heptanoate) is a branched/crosslinked polyester according to Figure 2 with shorter carbon chain (C6 – C10) end groups. The resulting polymer is fluid with a velvety texture and provides a similar function to castor oil in cosmetic formulations. The combination of the polar backbone and the hydrophobic character from the end groups provides for interaction with pigments resulting in even dispersion and flocculation prevention. This effect was demonstrated in two pigment dispersion tests where the viscosity was measured as an indicator of how well the base fluid wets the pigment. A lower viscosity measurement indicates better pigment wetting and this will translate to improved pigment dispersion in formulation. The results of the pigment dispersion test with Red No. 7 Calcium Lake at a 1:1 loading of pigment:dispersant is shown in Figure 5. 

The viscosity of the 699 dispersion was lower than the dispersions with castor oil, polyglyceryl-2 triisotearate, and diisostearyl malate. A pigment dispersion test with micronised zinc oxide at a 1:2 loading of pigment:dispersant was also conducted. The viscosity of the 699 dispersion was 8,000 cP , lower than the dispersions with trioctyldodecyl citrate (10,000 cP), pentaerythrityl tetraisostearate (90,000 cP), tridecyl trimellitate (235,000 cP), and dipentaerythrityl tripolyhydroxystearate (23,000 cP). The smooth and uniform dispersion appearance of micronised zinc oxide in 699 after manual mixing for approximately 3 minutes is shown in Figure 6. The dispersion uniformity during application was evaluated for 699 and isotridecyl isononanoate with coated and uncoated titanium dioxide, at a 2:1 loading of pigment:dispersant (Fig 7). Pigment dispersed with 699 has a smoother and more uniform appearance upon application with both variants of titanium dioxide.