What is #"Dacron"#?
Dacron is polyethylene terephthalate or PET. The monomer, therefore, is bis(2-hydroxyethyl) terephthalate.
Dacron is simply a brand name for polyethylene terephthalate. Please note that polyethylene terephthalate is not a copolymer, it is a homopolymer of bis(2-hydroxyethyl) terephthalate.
A copolymer would require two different monomers to react together during the process of polymerisation. This does not happen in the production of PET.
Its true that two different substances react together, but they are not monomers. They are simply reagents that react together to form the (single) monomer. The monomer then undergoes polymerisation to form the final homopolymer.
The monomer, bis(2-hydroxyethyl) terephthalate, is prepared either by reaction of ethylene glycol and terephthalic acid, or by the reaction of dimethyl terephthalate and ethylene glycol as a transesterification.