Video Transcript
Polyethylene terephthalate is a
condensation polymer that can be made from ethylene glycol and terephthalic acid
molecules. The following figure shows the
structures of the ethylene glycol and terephthalic acid molecules. What is the structure of the
polyethylene terephthalate condensation polymer?
Before we can determine the
structure of polyethylene terephthalate, we’ll need to clear some space. So let’s remove the answer choices
for now. Polyethylene terephthalate is a
polymer. A polymer is a chemical that can be
formed from similar chemical units called monomers that join together. More specifically, polyethylene
terephthalate is a condensation polymer. A condensation polymer is a type of
polymer that forms when bits of the monomers break off and the remainders bond
together. So the formation of a condensation
polymer is accompanied by the formation of small by-product molecules.
We are told in the question that
polyethylene terephthalate can be made from ethylene glycol and terephthalic acid
molecules. So polyethylene terephthalate is a
copolymer, a polymer produced from two or more different monomers. When terephthalic acid and ethylene
glycol react, the terephthalic acid monomer loses a hydroxy group. The ethylene glycol monomer loses a
hydrogen atom. The two monomer pieces join
together using an ester linkage, and the byproduct water is produced. The end of each monomer can go on
to react further. The monomers can continue to react
increasing the length of the polymer.
Looking at the polymer, we can see
that the same unit will repeat over and over in the polymer chain. We can represent the structure of a
polymer by writing the repeating unit in brackets followed by a subscript letter
𝑛. The 𝑛 indicates the number of
times the unit repeats in the polymer, which can vary and is often a very large
number.
Now that we know the structure of
polyethylene terephthalate, we can bring back the answer choices. We can see that the correct
structure of the condensation polymer polyethylene terephthalate is the structure
shown in answer choice (B).
