Problem 88 - Chemistry: The Central Science in SI Units, Global Edition

Question

Write the chemical equation that represents the formation of (a) polychloroprene from chloroprene (polychloroprene is used in highway- pavement seals, expansion joints, conveyor belts, and wire and cable jackets) (b) polyacrylonitrile from acrylonitrile (polyacrylonitrile is used in home furnishings, craft yarns, clothing, and many other items).

Step-by-Step Solution

Answer

The chemical equation for the formation of polychloroprene from chloroprene is: \(n\underline{\phantom{xxx}}(CH_2=CCl-CH=CH_2)\rightarrow -(CH_2-CCl-CH-CH_2)_n- \) The chemical equation for the formation of polyacrylonitrile from acrylonitrile is: \(n\underline{\phantom{xxx}}(CH_2=CH-CN)\rightarrow -(CH_2-CH-CN)_n- \)

Step 1: First, we need to know the structure of the monomers, chloroprene and acrylonitrile. Chloroprene is a vinyl monomer with the formula CH2=CCl-CH=CH2. Acrylonitrile is another vinyl monomer with the formula CH2=CH-CN. #Step 2: Identify the reactive groups and polymerization mechanism#

Both chloroprene and acrylonitrile contain a reactive double bond (C=C), and they will undergo addition polymerization to form polymers through opening the double bond. #Step 3: Write the chemical equation for the formation of polychloroprene from chloroprene#

Step 2: Write the chemical equation

By breaking the double bond in chloroprene and creating a bond between repeated chloroprene molecules, we can write the equation for the formation of polychloroprene: \(n\underline{\phantom{xxx}}(CH_2=CCl-CH=CH_2)\rightarrow -(CH_2-CCl-CH-CH_2)_n- \) where n represents the number of repeating chloroprene units, and these units are connected through the former double bonds. #Step 4: Write the chemical equation for the formation of polyacrylonitrile from acrylonitrile#

Step 3: Write the chemical equation

By breaking the double bond in acrylonitrile and creating a bond between repeated acrylonitrile molecules, we can write the equation for the formation of polyacrylonitrile: \(n\underline{\phantom{xxx}}(CH_2=CH-CN)\rightarrow -(CH_2-CH-CN)_n- \) where n represents the number of repeating acrylonitrile units, and these units are connected through the former double bonds.

Key Concepts

Polychloroprene

Polychloroprene is a versatile synthetic rubber that is widely used in various applications due to its resistance to weather, oil, and chemicals. It is synthesized through the polymerization of chloroprene, which is a vinyl monomer. This material is commonly found in items such as highway-pavement seals, expansion joints, and conveyor belts. It is also essential in the manufacturing of wire and cable jackets, adding to its industrial importance.
Polychloroprene is a product of addition polymerization. This process involves linking together chloroprene (chemical formula: CH2=CCl-CH=CH2) units by breaking the double bonds between carbon atoms and creating long chains. These newly formed chains result in the polymer polychloroprene, characterized by its distinct stability and robustness. In the polymerization reaction, n chloroprene molecules join to form polychloroprene, expressed as \(n\underline{\phantom{xxx}}(CH_2=CCl-CH=CH_2)\rightarrow -(CH_2-CCl-CH-CH_2)_n-\).
This chemistry makes polychloroprene useful in environments where durability is crucial. Its ability to withstand adverse conditions makes it a preferred choice for industrial and outdoor applications.

Polyacrylonitrile

Polyacrylonitrile is a crucial synthetic fiber used extensively in the textile industry due to its high strength and thermal stability. It is made from the monomer acrylonitrile, another type of vinyl monomer. This polymer is used in home furnishings, craft yarns, and clothing, among other items, due to its favorable properties.
Like polychloroprene, the formation of polyacrylonitrile involves addition polymerization. This mechanism involves the monomer acrylonitrile, which has the formula CH2=CH-CN. During polymerization, the double bond in acrylonitrile is broken, leading to the creation of long polymer chains. This transformation is represented by the equation \(n\underline{\phantom{xxx}}(CH_2=CH-CN)\rightarrow -(CH_2-CH-CN)_n-\), where n signifies the number of repeating acrylonitrile units.
Polyacrylonitrile is highly valued for its performance characteristics such as resilience, resistance to chemicals, and resistance to fire. These features make it an essential component in manufacturing a wide range of textile products.

Vinyl Monomers

Vinyl monomers are a type of simple alkene derivatives characterized by the presence of a double bond between two carbon atoms in their chemical structure. This functional group is notably reactive, facilitating polymerization reactions where monomers are linked together to form polymers. Both chloroprene and acrylonitrile are examples of vinyl monomers.
Vinyl monomers are critical in forming synthetic polymers through processes such as addition polymerization. They act as building blocks, connecting via their reactive double bonds. This connectivity allows for the assembly of complex materials with specific properties. The structural arrangement of vinyl monomers plays a significant role in determining the characteristics and functionalities of the resulting polymers.
In industry, the versatility of vinyl monomers supports the creation of a variety of polymer products with applications ranging from industrial materials to consumer goods. The ongoing exploration and manipulation of these monomers continue to drive innovation in materials science.

Addition Polymerization

Addition polymerization is a fundamental process in polymer chemistry where monomers engage in a chain reaction to form polymers. This type of polymerization is characterized by the use of unsaturated monomers, specifically those containing double bonds like vinyl monomers, which include chloroprene and acrylonitrile.
The reaction mechanism starts with the initiation step, where the double bond of the monomer is opened, creating active sites. These active sites are propagated through chain reaction steps, consecutively adding monomer units to form long polymer chains. Importantly, no by-products are formed during addition polymerization, making it a clean and efficient method.

• Initiation: Breaking of the double bond to form reactive sites.
• Propagation: Continuous addition of monomers to the growing chain.
• Termination: Chain growth ceases, usually when active sites are deactivated or combined.

This process is used extensively in industrial production because it allows for the customization of polymer properties by altering monomer types and polymerization conditions. Understanding addition polymerization is key to developing new materials and optimizing existing products in fields ranging from textiles to plastics. The polymers produced by this method, such as polychloroprene and polyacrylonitrile, are essential for numerous everyday and industrial uses.