Polyester

Category of polymers, in which the monomers are joined together by ester links

Polyester is a category of polymers that contain one or two ester linkages in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include some natural products, such as those found in plants and insects.

From Wikipedia, under CC BY-SA. More on occurri.