Animated Solution for Chemistry - Polymers: Which of the following is a condensation polymer?

When we dive into the fascinating world of polymers, one of the first and most crucial distinctions we must make is how these giant molecules are actually built. Imagine you are tasked with creating a long chain. You have two methods at your disposal. The first method is simply linking the pieces together, end to end, without losing any part of the original pieces. This is the essence of Addition Polymerization.

However, there is a second, more intricate method. Imagine that to link two pieces together, you have to snap off a tiny fragment from the ends of each piece. When they join, that tiny fragment falls away. This is the heart of Condensation Polymerization. In chemical terms, condensation polymers are formed by repeated condensation reactions between two different bi-functional or tri-functional monomeric units. The hallmark of this process is the elimination of small molecules, most commonly water ($H_{2}O$), but sometimes alcohol or hydrogen chloride.

Our mission is to identify the condensation polymer among the given options: Nylon-6,6, Neoprene, Teflon, and Buna-S. Let's put them under the microscope.

Let's start with Nylon-6,6. To understand how it's made, we need to look at its building blocks, its monomers. Nylon-6,6 is synthesized from two distinct monomers: Adipic acid and Hexamethylenediamine.

Adipic acid has the structure $\text{HOOC}-({\text{CH}}_2{)}_4-\text{COOH}$. Notice the two carboxylic acid groups at either end. It is a bi-functional molecule. Hexamethylenediamine has the structure ${\text{H}}_2\text{N}-({\text{CH}}_2{)}_6-{\text{NH}}_2$. It boasts two amine groups, making it perfectly bi-functional as well.

When these two molecules meet under the right conditions, a beautiful chemical dance occurs. The hydroxyl ($-\text{OH}$) group from the carboxylic acid of adipic acid and a hydrogen atom ($-\text{H}$) from the amine group of hexamethylenediamine combine.

What do they form? Water! This water molecule is eliminated from the system. In its place, a strong amide linkage ($-\text{CO}-\text{NH}-$) is forged between the carbon of the acid and the nitrogen of the amine.

The overall reaction looks like this:

Because this polymerization process inherently involves the continuous elimination of water molecules to build the polymer chain, Nylon-6,6 is a textbook example of a condensation polymer.

To be absolutely certain, let's quickly review the other candidates.

Neoprene is formed by the polymerization of chloroprene. Teflon is formed from tetrafluoroethylene. Buna-S is a copolymer formed from 1,3-butadiene and styrene.

In all three of these cases, the monomers contain double bonds. During polymerization, these double bonds break open, and the monomers simply add to one another to form the long polymer chain. There is absolutely no elimination of any small molecule. Therefore, they are all classified as addition polymers.

Our investigation is complete. Nylon-6,6 stands alone as the true condensation polymer in this lineup.