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Chapter 21: Problem 80

Polyesters containing double bonds are often crosslinked by reacting the polymer with styrene. a. Draw the structure of the copolymer of \(\mathrm{HO}-\mathrm{CH}_{2} \mathrm{CH}_{2}-\mathrm{OH} \quad\) and \(\quad \mathrm{HO}_{2} \mathrm{C}-\mathrm{CH}=\mathrm{CH}-\mathrm{CO}_{2} \mathrm{H}\) b. Draw the structure of the crosslinked polymer (after the polyester has been reacted with styrene).

Short Answer

Expert verified
The copolymer structure of \(\mathrm{HO}-\mathrm{CH}_{2} \mathrm{CH}_{2}-\mathrm{OH}\) and \(\mathrm{HO}_{2} \mathrm{C}-\mathrm{CH}=\mathrm{CH}-\mathrm{CO}_{2} \mathrm{H}\) is: \(\mathrm{OOC}-\mathrm{C}(\mathrm{HO})=\mathrm{CH}-\mathrm{COO}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{O}\). After crosslinking with styrene, the crosslinked polymer structure is: \(\mathrm{OOC}-\mathrm{C}(\mathrm{HO})=(\mathrm{C}_{6}\mathrm{H}_{5}-\mathrm{CH}_{2}-\mathrm{C})(\mathrm{OOC}-\mathrm{C}(\mathrm{HO})=\mathrm{CH}-\mathrm{COO}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{O})(\mathrm{CO}_{2}\mathrm{H})\), where styrene is the crosslinked point between the copolymer chains.

Step by step solution

01

Draw monomers

First, we draw the structures of the two monomers. 1. Monomer 1: \(\mathrm{HO}-\mathrm{CH}_{2} \mathrm{CH}_{2}-\mathrm{OH}\) (this monomer consists of a diol with hydroxyl groups on each end) 2. Monomer 2: \(\mathrm{HO}_{2} \mathrm{C}-\mathrm{CH}=\mathrm{CH}-\mathrm{CO}_{2} \mathrm{H}\) (this monomer is a dicarboxylic acid with a double bond)
02

Combine monomers to form copolymer

To create the copolymer structure, we can combine the two monomers using esterification reaction mechanism between hydroxyl groups (from monomer 1) and carboxylic acid groups (from monomer 2). The ester bond is formed via the elimination of a water molecule from the reaction. The copolymer structure: \(\mathrm{OOC}-\mathrm{C}(\mathrm{HO})=\mathrm{CH}-\mathrm{COO}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{O}\)
03

Draw the structure of styrene

In order to draw the structure of the crosslinked polymer, we need to understand the structure of styrene. Styrene: \(\mathrm{C}_{6}\mathrm{H}_{5}-\mathrm{CH}=\mathrm{CH}_{2}\)
04

Create the crosslinked polymer structure

For crosslinking, the double bond present in the copolymer will react with the double bond present in the styrene via free radical polymerization. Crosslinking occurs when the styrene molecules react with multiple double bonds along the copolymer chain. To create the crosslinked polymer structure, we can combine the copolymer (from step 2) and styrene (from step 3). In this reaction, the radical from styrene will bind to the double bond present in the copolymer, joining two copolymer chains to form a 3D structure. Crosslinked points will occur wherever a styrene molecule reacts with the double bonds along the copolymer chains. The crosslinked polymer will look like this: \(\mathrm{OOC}-\mathrm{C}(\mathrm{HO})=(\mathrm{C}_{6}\mathrm{H}_{5}-\mathrm{CH}_{2}-\mathrm{C})(\mathrm{OOC}-\mathrm{C}(\mathrm{HO})=\mathrm{CH}-\mathrm{COO}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{O})(\mathrm{CO}_{2}\mathrm{H})\) Here, the styrene (\(\mathrm{C}_{6}\mathrm{H}_{5}-\mathrm{CH}_{2}-\mathrm{C}\)) is the crosslinked point between the copolymer chains.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Polyester Formation
Polyesters are a class of polymers formed through a condensation reaction between a diol and a dicarboxylic acid. In this specific example, the first monomer is ethylene glycol (\(\mathrm{HO}-\mathrm{CH}_{2} \mathrm{CH}_{2}-\mathrm{OH}\)), and the second is maleic acid (\(\mathrm{HO}_{2} \mathrm{C}-\mathrm{CH}=\mathrm{CH}-\mathrm{CO}_{2} \mathrm{H}\)). Through an esterification reaction, these monomers are linked.
  • **Esterification**: This reaction joins monomers by forming ester bonds. A water molecule is released when a hydroxyl group from the diol reacts with a carboxylic group from the dicarboxylic acid.
  • **Copolymers**: This process results in the formation of a copolymer, which consists of repeating units from both monomers.
This form of polymerization creates a linear polymer chain. Each link in the chain is an ester group, which is why this process is known as polyester formation. The structure of the copolymer contains double bonds, which are crucial for later reactions like crosslinking.
Crosslinking
Crosslinking in polymers refers to the creation of chemical links between different polymer chains. These links can enhance the material's properties, such as strength and heat resistance. In this exercise, crosslinking involves styrene.
  • **Styrene**: This monomer, \(\mathrm{C}_{6}\mathrm{H}_{5}-\mathrm{CH}=\mathrm{CH}_{2}\), adds rigidity and strength when it forms these links.
  • **Crosslinked Structure**: When styrene reacts with the double bonds in the polyester, it creates a three-dimensional network. This network hinders the movement of polymer chains, making the material more rigid and resistant to external forces.
Styrene contributes a phenyl ring, which adds further strength due to its bulky structure, making crosslinked polyesters often used in applications where durability is critical, like car parts and construction materials.
Free Radical Polymerization
Free radical polymerization is a method of polymer formation that involves the use of free radicals to initiate a chain reaction of monomers. In the given context, it is used to initiate the crosslinking process between the copolymer and styrene.
  • **Free Radicals**: These are highly reactive molecules with an unpaired electron. They can start a polymerization process by attacking the double bonds in the monomers, which makes new bonds while generating more radicals in the process.
  • **Initiation Step**: Typically, a radical initiator breaks down under heat or light to produce free radicals. Once the radicals are formed, they react with the double bonds in the styrene and the copolymer.
  • **Propagating the Reaction**: As radicals continue to attack new double bonds, the polymer chain grows, and more polymer chains crosslink. The process proceeds until all active monomer sites are exhausted or terminated.
This method efficiently creates densely crosslinked polymers, providing materials with excellent mechanical properties and chemical resistance. Free radical polymerization is thus an essential technique for enhancing the properties of polymeric materials.

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Most popular questions from this chapter

Three different organic compounds have the formula \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}\). Only two of these isomers react with KMnO_ (a strong oxidizing agent). What are the names of the products when these isomers react with excess \(\mathrm{KMnO}_{4} ?\)

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