What molecular structural features cause high-density polyethylene to be denser than low-density polyethylene?

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Welcome back everyone in this example, we need to determine what makes high density polyethylene denser than low density polyethylene based on their molecular structure. So we want to recall the shorthand for high density poly ethylene and then we have low density polyethylene defined as the following. And so when it comes to high density polyethylene, we want to recall that we have a very stiff and hard linear structure, so that's just going to appear as follows. And let's make low density polyethylene a different color. So going back to high density polyethylene as we stated, it's a very stiff, hard linear structure. So these are the many chains of high density polyethylene. And we want to recognize that these are un branched linear chains again. Whereas on the contrary, we have low density polyethylene, which is where we have a tough but flexible branched structure. So we have these tough, flexible branched structure chains of low density polyethylene. Now, because our high density polyethylene has these un branched linear chains that are much longer than low density polyethylene. These un branched linear chains are going to fit closer together so we can see that here they fit closer together, we'll say the chains fit closer together and so therefore they have more rigid or let's say more crystalline and by that we mean ordered and aligned regions due to this close packing of our high density polyethylene. And that means we can confirm that low density polyethylene is less crystalline and is less packed together because it's more flexible. So we'll say that low density polyethylene has a low crystalline itty. Now for our final answer for what makes high density polyethylene denser than low density polyethylene based on the molecular structure. We're going to confirm that this is due to its un branched linear chains that fit closer together. And so what's highlighted in yellow confirms as to why high density polyethylene has a greater density than our low density polyethylene. So what's highlighted in yellow is our final answer. I hope everything I reviewed was clear. If you have any questions, leave them down below and I will see everyone in the next practice video.

What molecular structural features cause high-density polyethylene to be denser than low-density polyethylene?

Verified Solution

Key Concepts

Polyethylene Structure

Density and Molecular Packing

Crystallinity in Polymers