Step-Growth Polymers - Online Tutor, Practice Problems & Exam Prep

Step growth polymers, often condensation polymers, form through the combination of bifunctional monomers in a series of steps, creating dimers, trimers, and ultimately long polymer chains. Key reactions include nucleophilic acyl substitution mechanisms for amides, esters, and polyamides, while polyurethanes and epoxy resins involve different mechanisms. Understanding these reactions is crucial for grasping polymer chemistry, as they illustrate the formation of various polymer types through specific functional group interactions and condensation processes, emphasizing the importance of monomer functionality in polymer synthesis.

Step-Growth Polymers Concept 1

In this video, let's talk about step growth polymers. Now we're going to say here that many step growth polymers represent what we call condensation polymers. But we're calling that a step growth polymer forms fragments, which combine in steps to form our polymer. So if we take a look here, we have individual monomers. And we're going to say that these monomers can link up together, forming dimers or even trimers or, in some cases, even tetramers.

These then link up together, and they're going to form a polymer in steps. Now, here we're going to say that a condensation polymer is just a linear polymer that is formed from a bifunctional monomer. So step growth polymers are the umbrella idea. And then, when we go even deeper, more specific, we're looking now at condensation polymers. These are only linear polymers, and we're going to look at the bifunctionality of the monomers involved in creating them.

Step-Growth Polymers Concept 2

In this video, we're going to take a look at the different types of step growth polymerization reactions. Now we're going to say depending on the starting materials, there are 5 major step growth polymerization reactions. If we take a look at the first three, notice that they're all shaded in green. That's because they're all going to follow a similar nucleophilic acyl substitution mechanism. So if we look, we have alcohols with amines, which can make amides.

We have carboxylic acids with alcohols, which can make esters. We have acyl chlorides with alcohols, which could help us to make yet another type of ester. And then we're going to say that the bottom 2 are shaded differently because unlike the top 3, they don't follow a typical nucleophilic acyl substitution mechanism. They do their own thing. They can do nucleophilic addition reactions and some type of SN2 reactions.

We'll talk about them later on in greater detail, but remember we can group them all together because they all are dealing with bifunctional monomers. So if we take a look, bifunctional because we have what? Diols and diamines that we see here. So we take a look. We're going to see a polyamide formation.

We have a diacid. We have a diamine. Remember, we're going to have dehydration going on here or condensation going on here where we lose water. The simplest way to think about it is we have an NH here, connecting, and then we have another NH here. Here we put this in brackets and an x to show that this chain could be really long.

It doesn't necessarily have to be 1 carbon long. Next, we have polyester formation. So here we have our carboxylic acid ends and we have alcohols. Again, we have loss of water in this process and brackets. So here we make our polyester.

And again, this is just a super simplified way of looking at this. If you don't recall the mechanisms for nucleophilic substitution, make sure you go back and take a look. Look under the section of carboxylic acid derivatives. So here we have phosgene, which is a carbonyl with 2 chlorines, and we have a diol yet again. We have the loss of HCl here.

So here what we create is we're going to create we'd have this phosgene involved. So we're going to say here we have O, O, and there it goes right there. There goes our structure. And these all actually come from the diol. So we'd have this structure here, and doing that creates a polycarbonate.

Now here we have polyurethane formation. Here the typical type of structures that we're dealing with are toluene, diisocyanate. We'll go in greater detail on that later on, but for right now, just realize diisocyanate, we have 2 isocyanate groups. Toluene is just a benzene with a methyl group. So those are our 3 substituents.

And we're going to say here that this think about in the simplest terms, some type of addition reaction. Here, I'm just showing a simplified way of looking at it. This is not the actual mechanism. It's just a way of interpreting this on how we create our polyurethane at the end. So we could say here that this nitrogen with its lone pairs, this lone pair could grab this hydrogen here, and this bond here can break Going here, causing this bond to break here and then later on it's protonated.

Alright. So doing that here would give us what? It would give us this structure at the end. It's a little bit different but we have this, x, and then O here. So this is the structure we'd make at the end.

Alright. Then we'd have, lastly, epoxy resin formation. So here we have an epichlorohydrin. So here's our structure. And then we're reacting it with specifically BPA, which is Bisphenol A, so it's 2 benzenes and they're both phenols.

They're both connected to the same carbon which has 2 methyl groups off of it. Okay. So this is BPA. Now here, these connect together, and this is found here in the middle. It comes out as this.

So we have this oxygen, which is part of our BPA, and it's going to be connected here to this. Now what's in black is this epichlorohydrin. So this is just an overview of what it looks like. Right? Now if you do have this based on your textbook, you'll see later on how this occurs.

Right? For those of you who don't have to worry about this mechanism, just realize that this is just one of the 5 different types of step growth polymerization reactions that are out there, and I'm just showing how they can combine together to make epoxy resin. Yet another type of polymer. Alright. So here are 5 reactions.

Just keep in mind what we've seen. The first three are reminders of our nucleophilic acyl substitution reactions we saw earlier with carboxylic acid derivatives. And these bottom 2 are a little bit different.

Step-Growth Polymers Example 1

Hey, everyone. So here it says to draw the polymer created when phosgene reacts with 2 moles of 1,5-pentanediol. Alright. So phosgene represents this, and we're reacting with 2 moles of 1,5-pentanediol. So 1, 2, 3, 4, 5, OH.

1, 2, 3, 4, 5, and then OH. We know that we're going to have the loss of HCl in some way. We're not worrying about the mechanism here because, one, I didn't ask for it, and two, we know that this is going to follow our typical nucleophilic acyl substitution mechanisms that we saw within the carboxylic acid derivatives chapter. So if you need a refresher, make sure you go back there and take a look at that mechanism. Here, we're just worrying about what we're going to make at the end, which is our polymer.

So here we have our carbonyl, and it's going to be connected to the oxygens. And then 1, 2, 3, 4, 5, then OH, and then oxygen here. 1, 2, 3, 4, 5, and then OH. So this would represent our polymer that's created from reacting phosgene with our 2 moles of 1,5-pentanediol.

Provide the polymer created from the reaction of malonic acid and 1,4-dihydroxybenzene.

Here it says, provide the polymer created from the reaction of malonic acid and 1,4-dihydroxybenzene. Alright. So here, remember malonic acid, we kinda know what that looks like because remember we know what our malonic ester synthesis is. So we have 2 carbonyl groups, with carbons separating them. And it's an acid, so we're talking about the carboxylic acid form. And we're reacting this with our 1,4-dihydroxybenzene. So we're gonna have here 1,4-dihydroxybenzene. Alright. So here we're gonna say, when this reacts, we know we're gonna have the loss of water. Right? Lose water there. So we know we're gonna form something. Right. So we're gonna show that. Right. Now we know what's connected to this benzene here. And we can say that it connects to another one of these. We're just not showing the other ends; we're just focusing on that segment of the polymer. This is what we would make as a result of this reaction between our malonic acid and 1,4-dihydroxybenzene. Right? So, again, we're not paying attention to the mechanism, because we didn't ask for it. And we know that this is gonna form our polyester, and it follows a nucleophilic acyl substitution mechanism. Make sure if you don't remember how that works to go back and take a look at our carboxylic acid derivatives chapter.

Determine the monomers involved in the construction of the following polyamide.

In this practice question, it says to determine the monomers involved in the construction of the following polyamide. Remember, a polyamide is formed through the reaction of a diacid and a diamine. So, if we take a look here, our diamine is this portion here and this portion here. So our diamine was NH2 (NH2) and then we have 1, 2, 3 carbons separating the NH2 groups. So there goes our diamine. And then our diacid portion has to be this. Right. So that was 2 carboxylic acids separated by 2 carbons. And so, to form this polyamide, we reacted this diacid with this diamine. So those represent our monomers from the beginning.