Polyquaternium-91 is a chemical compound, quaternised polymer, is a polymeric quaternary ammonium salt of hydroxypropyl methacrylate and polyethylene glycol methacrylate quaternized with ethyltrimonium chloride methacrylate
It occurs as a colourless to light yellow liquid, soluble in water, insoluble in ester, hydrocarbons and ketone or in the form of a white powder.

What it is used for and where
Cosmetics
Film-forming agent. Produces a very thin continuous film with an optimal balance of cohesion, adhesion and adhesiveness on skin or hair.
Hair conditioning agent. A large number of ingredients with specific purposes can co-exist in a hair shampoo: cleansers, conditioners, thickeners, mattifying agents, sequestering agents, fragrances, preservatives, special additives. However, the indispensable ingredients are the cleansers and conditioners as they are necessary and sufficient for hair cleansing and manageability. The others act as commercial and non-essential auxiliaries such as: appearance, fragrance, colouring, etc. Hair conditioning agents have the task of increasing shine, manageability and volume, and reducing static electricity, especially after treatments such as colouring, ironing, waving, drying and brushing. They are, in practice, dispersing agents that may contain cationic surfactants, thickeners, emollients, polymers. The typology of hair conditioners includes: intensive conditioners, instant conditioners, thickening conditioners, drying conditioners.
Surface modifier. Substance that has the property of preventing superficial defects in the epidermis by repelling oils and water and of giving the skin greater resistance against blemishes.
Synonyms: Ethanaminium, N, N, N-trimethyl-2-[(2-methyl-1-oxo-2-propeny-1-yl)oxy]-, chloride (1:1), polymer with α-(1-oxo-2-propen-1-yl)-θ-hydroxypoly(oxy-1,2-ethanediyl) and 1,2-propanediol mono(2-methyl-2-propenoate)
CAS: 1020103-28-9