Animated Solution for Chemistry - Organic Chemistry: The correct name of the following polymer is

When we encounter a polymer structure, the first step is always to identify its repeating unit. Imagine the polymer as a long train; the repeating unit is the single boxcar that gets duplicated over and over again.

In our given structure, the repeating unit is enclosed within brackets, denoted by the subscript $n$. It consists of a $-{\text{CH}}_2-$ group bonded to a central carbon atom, which is further attached to two methyl ($-{\text{CH}}_3$) groups.

Notice that the entire backbone of this polymer consists solely of carbon atoms connected by single bonds. This is a massive clue! It tells us that this is an addition polymer, formed without the loss of any small molecules like water or ammonia.

Finding the Monomer

To name the polymer, we must first unmask its secret identity: the monomer. Since it's an addition polymer, the single bonds connecting the repeating units were originally a double bond in the monomer.

Think of it as reverse engineering. If we break the bonds extending outside the brackets and fold those electrons back in, we restore the double bond between the two main-chain carbon atoms.

This simple mental exercise transforms our repeating unit, $-{\text{CH}}_2-\text{C}({\text{CH}}_3{)}_2-$, back into its original monomeric form: ${\text{CH}}_2=\text{C}({\text{CH}}_3{)}_2$.

Now that we have our monomer, ${\text{CH}}_2=\text{C}({\text{CH}}_3{)}_2$, we need to name it.

According to IUPAC nomenclature, the longest chain containing the double bond has three carbon atoms (propene), and there is a methyl group on the second carbon. So, the systematic name is 2-methylpropene.

However, the polymer industry loves its common names! This specific branched arrangement of four carbon atoms containing a double bond is universally known as isobutylene.

The naming convention for addition polymers is beautifully straightforward: you simply take the name of the monomer and slap the prefix "poly-" in front of it.

Since our monomer is isobutylene, the resulting polymer is polyisobutylene.

This polymer is incredibly useful in the real world. Because of its tightly packed structure, it is highly impermeable to gases, making it the perfect material for the inner tubes of tires and basketballs!