Polymer Stereochemistry - Online Tutor, Practice Problems & Exam Prep

Polymers exhibit diverse stereochemistry, characterized by the arrangement of chiral centers along their chains. The three primary configurations are isotactic, where all side groups (R) are on the same side; syndiotactic, where R groups alternate sides; and atactic, where R groups are arranged randomly. The polymerization conditions significantly influence these stereochemical outcomes, impacting the physical properties and applications of the resulting polymers. Understanding these configurations is crucial for manipulating polymer characteristics in various chemical and industrial processes.

Polymer Stereochemistry Concept 1

Hey, everyone. So in this video, let's talk about polymers and their stereochemistry. Now here, we're going to say that linear polymers possess a large number of chiral centers and that there are 3 types of stereochemical configurations that are possible. Now depending on our spatial orientation of side groups, which we're going to label as r, along the polymer chain, we can have isotactic, syndiotactic, and atactic. Now with isotactic, we're going to say r groups on the same side of the polymer chain.

So here, let's just say all of them would be wedged. So this polymer will be isotactic. Next, we have syndiotactic. So we're going to say our groups regularly alternate sides. Let's say we have wedged then alternates to dashed then wedged again and then dashed.

The pattern is basically it's we can see it and we can predict what the next one's going to be. But then we have atactic, and we're going to say our groups oriented randomly. Let's say this is wedged. This is wedged. But then, hey, we get a dashed.

And then, hey, we go back to wedged. So it's random. Now we're going to say polymerization conditions result in different stereochemistries. So just remember when it comes to these orientations, there are 3 of them here. We have isotactic, syndiotactic, and atactic.

Polymer Stereochemistry Example 1

In this example, it says to indicate whether each polymer rotates plane polarized light with 'y' for yes or 'n' for no. Remember, if you're going to rotate plane polarized light, that means you are chiral in nature. So if we take a look at the first one, this will be a 'no' because all these carbons, yes, they have chlorines with stereochemistry, but they're not chiral because they're not connected to 4 different groups. Each of them are connected to 2 chlorines. And the same thing with these methylene carbons, these CH₂ carbons, they're also connected to 2 hydrogens.

Now let's go to b. If we imagine that we can cut this in half, you would see that this side here looks like this side as though they're looking at each other in a mirror. There's an internal plane of symmetry, similar to what we learned about meso compounds. So here we'd say 'no'. Over here, again, if we just imagine there's a mirror right there.

Right? And we're looking on both sides here, we would say 'no'. And then this one here, this is random. Both sides don't look the same. So this would be chiral still.

So this would be a 'yes'. Alright. So that's how we'd approach each one of these polymers to determine if they're rotating plane polarized light, meaning they are chiral.

Draw a segment of syndiotactic polymer of vinyl chloride. 

Here it says, draw a segment of syndiotactic polymer of vinyl chloride. So vinyl chloride means you have an alkene connected to a chlorine. And we would say the way this works is if we're trying to draw the polymer, so we'd have here are different let's see how much we're going to do this. This, three, we'll do this. Alright. So then we're going to say here that we have syndiotactic, which means we have a predictable pattern that we can see it's alternating. So we have a chlorine here, let's say it's dashed, then it alternates to wedged, then it alternates back to dashed, then it alternates to wedged. So this could represent a segment of a syndiotactic polymer of vinyl chloride.