Question Video: Physical Properties of Polymers

Video Transcript

Polymers can have varying physical properties. Which of the following is an unlikely property of a polymer? Flexible, strong, stiff, gaseous, or elastic.

This question is asking us about polymers. So let’s review what we already know about what a polymer is. A polymer is a very large molecule which is made by joining lots of smaller molecules together. You may hear that these smaller molecules are referred to as monomers. So you can imagine this process like building a chain from lots of blocks. Each block being a monomer and the resulting chain a polymer. Bear in mind that not all polymers are straight chains, like the one I’ve drawn here. And not all polymers are made from just one type of monomer. They could be built from a mixture.

Now let’s take a look at the properties we’ve been given. Let’s start with the first one, flexible. What we have to decide is, can a polymer be flexible? What we mean by flexible is that we can bend the polymer without it breaking. Because polymers are such long-chain molecules, they can quite easily be bent. Let’s think of some real-life examples where this is the case. For example, consider low-density polyethylene, or LDPE. This material is used to make lots of flexible things, for example, plastic wrapping, bags, and six-pack rings. So flexibility is a likely property of polymers, so isn’t the correct answer to this question.

So, let’s move on to looking at a strong polymer. Polyvinyl chloride or PVC, for example, is often used to make things like doors and windows. PVC is very strong and durable, although if you want to make it more flexible, you can add plasticizers to add that property. There are many other examples of polymers, which are very strong. So this is not a correct answer.

Now let’s look to see if polymers can be stiff. If something is stiff, it means that we can’t easily bend it. This is the opposite of something being flexible. We could for example cross-link two polymer chains. This means forming bonds between the chains. Doing this results in a very stiff, strong material. For example, the process of vulcanizing rubber involves cross-linking and results in a stronger stiffer material. So this could be a property of a polymer. This means it’s not the correct answer to our question.

So let’s move on to gaseous. For a material to be in the gas phase at room temperature, the molecules are usually very small. Think about nitrogen as a gas, N₂, or carbon dioxide, CO₂. Both of these examples are very small molecules. Polymers, on the other hand, are very large molecules, often very long and sometimes branched. In order to turn these into a gas, you would need to introduce a lot of heat, which would likely break down the polymer. So it’s very unlikely that you’re going to have a polymer in a gaseous phase. So this is a good candidate for the right answer to this question. But let’s check the last one, just to be safe.

So can a polymer be elastic? It turns out that there’s a whole category of polymers which demonstrate elasticity. They’re even given their own name, elastomers. In an elastomer, there are generally very weak forces in between the polymer chains. This means that you’re able to stretch them. An example of an elastomer like this is the sort you would find in a rubber band, for example. So polymers can be elastic. So this is not the right answer. So of these five properties, the only one which is unlikely to be a property of a polymer is the fourth one, gaseous.