Polyquaternium-59 is a chemical compound, copolymer, the polymeric quaternary ammonium salt.
Poly(20,25-dioxo-2,5,10,15,18-pentamethyl-10-(2-hydroxy-3-(3-(3-phenyl-2-propenamido)propyldimethylammonio)propyl)-10-azonia-1,4,7,13,16,19-hexaoxapentacosanediyl) chloride
The number after Poliquaternium is a chronological reference of the registration date of this ingredient.
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
Photostabiliser. It’s a chemical compound that absorbs UV radiation and dissipates absorbed energy in a harmless form like heat or radiation.