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Ch.8 - Reactions of Alkenes
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.8 - Reactions of AlkenesProblem 73
Chapter 8, Problem 73

When styrene (vinylbenzene) is commercially polymerized, about 1–3% of 1,4-divinylbenzene is often added to the styrene. The incorporation of some divinylbenzene gives a polymer with more strength and better resistance to organic solvents. Explain how a very small amount of divinylbenzene has a marked effect on the properties of the polymer.

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Step 1: Understand the structure of styrene and 1,4-divinylbenzene. Styrene (vinylbenzene) has a benzene ring with a single vinyl group (-CH=CH2) attached. 1,4-divinylbenzene has a benzene ring with two vinyl groups attached at the 1 and 4 positions.
Step 2: Recognize the role of 1,4-divinylbenzene in polymerization. During polymerization, the vinyl groups in styrene undergo a chain-growth polymerization to form long polymer chains. The presence of 1,4-divinylbenzene introduces additional vinyl groups that can form cross-links between different polymer chains.
Step 3: Explain the concept of cross-linking. Cross-linking occurs when the vinyl groups on 1,4-divinylbenzene react with the growing polymer chains, creating covalent bonds between separate chains. This results in a three-dimensional network structure rather than linear polymer chains.
Step 4: Discuss the impact of cross-linking on polymer properties. The cross-linked structure restricts the movement of polymer chains, making the material more rigid and less prone to deformation. This enhances the strength and resistance to organic solvents of the polymer.
Step 5: Conclude by emphasizing the significance of small amounts of 1,4-divinylbenzene. Even a small percentage of 1,4-divinylbenzene can create enough cross-links to significantly alter the polymer's mechanical and chemical properties, leading to improved performance in commercial applications.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Polymerization

Polymerization is the chemical process in which small molecules, known as monomers, combine to form a larger, more complex structure called a polymer. In the case of styrene, the polymerization process leads to the formation of polystyrene, a widely used plastic. The addition of a cross-linking agent like divinylbenzene during polymerization can significantly alter the physical properties of the resulting polymer.
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Cross-linking

Cross-linking refers to the formation of chemical bonds between polymer chains, which can enhance the strength and stability of the material. When divinylbenzene is added to styrene, it acts as a cross-linker, creating connections between polystyrene chains. This results in a three-dimensional network structure that improves the mechanical properties and solvent resistance of the polymer.
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Thermal and Chemical Resistance

Thermal and chemical resistance are critical properties of polymers that determine their performance in various environments. The incorporation of divinylbenzene into the polymer matrix increases the density of cross-links, which enhances the material's ability to withstand heat and exposure to organic solvents. This makes the modified polymer more durable and suitable for applications requiring higher performance under challenging conditions.
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Related Practice
Textbook Question

Propose a mechanism for reaction of the first three propylene units in the polymerization of propylene in the presence of a peroxide.

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Textbook Question

Ozonolysis can be applied selectively to different types of carbon–carbon double bonds. The compound shown below contains two vinyl ether double bonds, which are electron-rich because of the electron-donating alkoxy groups. Ozone reacts more quickly with electron-rich double bonds and more slowly with hindered double bonds. At −78 °C, this compound quickly adds two equivalents of ozone. Immediate reduction of the ozonide gives a good yield of a single product. Show the expected ozonolyis product, and label the functional groups produced, some of which are not typical from ozonolysis of simple alkenes.

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Textbook Question

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Textbook Question

Propose mechanisms to explain the opposite regiochemistry observed in the following two reactions.

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