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Polymers in Personal Care
By: Eric Abrutyn, TPC2 Advisors Ltd., Inc.
Posted: June 28, 2010, from the July 2010 issue of Cosmetics & Toiletries.
Polymer use began in the 1800s with cellulose derivatives, the vulcanization of rubber, and styrene synthesis; but in reality, it started more than four million years ago with the formation of DNA and proteins. Polymers are a diverse class of chemistry. By definition, they are large molecules made up of chains or rings of linked monomer units—simple reactive building blocks. Smaller molecules or monomers are combined to form polymers that possess a characteristic chain structure of multiple repeating units that can be related or different.
While similar polymers can be grouped into classifications, they often still differ somewhat in structure, performance or their main component(s). As a result, not all same-named polymers are necessarily the same in performance or structural morphology. Typically the side groups on the backbone of a polymer influence its functional properties, even when present in small molar percentages. Understanding what side groups are attached and where will allow one to better understand the potential impact of the pendent side groups to the molecule’s functionality—and will thus assist the formulating chemist in choosing the proper ingredient for the desired results.
Polymers in the personal care industry are also categorized by a number of classifications in the International Nomenclature Cosmetic Ingredient (INCI) dictionary, including: organic polymers, inorganic polymers, siloxane polymers and naturally occurring polymers. These classifications generally are further divided into sub-classes: homo-polymers, copolymers, cross-linked polymers, mixed classification polymers, dendrimers, natural-sourced polymers and synthetic peptides. Polymer nomenclature assignment is based upon standard references such as the material’s CAS number, the International Union of Pure and Applied Chemistry (IUPAC), Merck, the Food Index, or generic INCI nomenclature—e.g., polyquaternium, polyacrylate, etc.
Due to the high efficacy of polymers, they typically are used in small quantities to exert various functions in formulations, including acting as: rheology modifiers, e.g., thickeners; surface active modifiers such as surfactants, emulsifiers and wetting agents; solubility modifiers including coupling agents and dispersants; bulking agents; preservatives; skin and hair conditioners; sunscreen agents; film-formers; aesthetic modifiers; coating agents/encapsulants; and abrasives/exfoliants. The subject matter is so complex and dynamically evolving that no one source can properly address the entire topic. The following is a tutorial meant to provide a starting point to help sort out the types of polymers along with their potential physical and chemical properties.
The IUPAC has devised a systematic set of rules for classifying polymers but the names can be cumbersome. Therefore, each industry shortens the names for simplicity’s sake and these shortened names eventually becoming common usage names. As noted, the architecture of a polymer typically affects physical, functional and/or chemical properties. The chains can be structured in multiple ways—including linear, branched, side chains, star polymers, comb polymers, brush polymers, dendronized polymers, ladders and cross-linked polymers—with a varying range of average molecular weights. Synthetic copolymers are seldom exactly defined sequences of many repeat units since there are an infinite number of ways to sequence two or more monomers along a polymer backbone (see Figure 1a–h).