Which of the following polymers has ester linkage?

Dacron (also known as polyethylene terephthalate or PET) is a condensation polymer formed by the reaction of ethylene glycol and terephthalic acid. Since it is formed by the condensation of an alcohol and a carboxylic acid, it contains ester linkages ($-COO-$) and is classified as a polyester.

Orlon (polyacrylonitrile), Teflon (polytetrafluoroethylene), and Neoprene (polychloroprene) are addition polymers and do not contain ester linkages.

Answer: Dacron