Small molecular weight solvents are sought in cosmetics, as it is challenging to find molecules that are efficient, safe for the skin and eyes, scarcely flammable, versatile, sensorially acceptable and compatible with most common cosmetic ingredients, all at the same time. This is why water, ethanol, glycerin and propylene glycols have been used for decades in most cosmetic formulas. Cosmetically acceptable lipophilic solvents are even rarer. In relation, one category of solvents with good potential for cosmetic applications is amphiphilic polyols. Polyols are alcohols containing multiple hydroxyl groups in their structure; these occur naturally in plants and animals, and also are produced synthetically.
The most active industries producing new low molecular weight molecules are those working with isoprene and terpenoid structures. In nature, isoprene moieties are the building blocks for many complex molecules like terpenes and natural rubber. For industrial applications like pharmaceutical intermediates, as well as solvent blends and paints, extensive investigations on the human and environmental safety of new small size molecules have been conducted.
Of these molecules, isopentyldiol (IPD) has survived scrutiny for potential skin sensitization and irritation, eye irritation, genotoxicity and toxicity to fish, Daphnia and aquatic plants. Being subject to Japanese standards for quasi-drug ingredients, it also has been rated highly in terms of safety. Its safety profile together with interesting sensory properties make it a novel candidate for the personal care industry. Here, the authors investigate its properties for cosmetics and personal care applications via tactile evaluations; tests, in combination with sorbitol, to restore smoothness in damaged hair; and a skin moisturization evaluation for its capability to increase skin moisture levels.
A unique one-step synthesis technology was used to prepare isoprene from the C4 fraction of naphtha cracking, which was then put through stringent purification processes to eliminate volatile odorous fractions, yielding an original hydrophilic polyol. IPD has an isoprene diol structure. Specifically, it is a branched chain bi-alcohol with a five carbon atom backbone, described by the formula: 3-methyl-1,3-butanediol. Due to its amphiphilic molecular structure, relatively small molecular size and the presence of two strategically positioned hydroxyl groups, it can form both intra-molecular and extended intermolecular hydrogen bonds, depending on the surrounding vehicle. It also has superior affinity to the skin and acts as a skin humectant and hydrotrope, as will be shown.