Problem 77 - A Complete Resource Book in Chemistry for JEE Main

Question

N repeating unit is made from which of the following monomer? (a) \(\mathrm{CH}_{2}=\mathrm{CHCN}\) (b) \(\mat… # Polyacrylonitrile, characterized by the CCCC#N repeating unit is made from which of the following monomer? (a) \)\mathrm{CH}_{2}=\mathrm{CHCN}\( (b) \)\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CN}\( (c) \)\mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\( (d) \)\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCN}$

Step-by-Step Solution

Answer

The monomer is (a) \\(\mathrm{CH}_{2}=\mathrm{CHCN}\\).

Step 1: Understanding the Question

We need to determine which monomer forms the repeating unit of polyacrylonitrile. The repeating unit of polyacrylonitrile is characterized by the cyano group (CCCC#N), which is a part of the structure of acrylonitrile.

Step 2: Analyzing Monomer Structures

Look at each option and determine if it has the structure necessary to form the repeating unit of polyacrylonitrile. Polyacrylonitrile is formed from acrylonitrile, which is denoted as \(\mathrm{CH}_{2}=\mathrm{CHCN}\). Here, \(\mathrm{CH}_{2}=\mathrm{CHCN}\) contains a double bond that allows polymerization and the cyano group (\(#N\)) that is needed.

Step 3: Matching the Structure

Compare the given options with the known monomer of polyacrylonitrile. Notice that only option (a) \(\mathrm{CH}_{2}=\mathrm{CHCN}\) contains both the double bond and the cyano group, matching the description of the polyacrylonitrile monomer.

Step 4: Confirming the Answer

Based on the analysis in the previous steps, option (a) is the only correct match for being the monomer unit of polyacrylonitrile, as it allows the formation of the polymer's repeating unit through polymerization.

Key Concepts

Polyacrylonitrile

Polyacrylonitrile (PAN) is a crucial polymer in the fabric and textile industries. This versatile material is known for its high strength and thermal stability, making it a perfect candidate for applications such as synthetic fibers and carbon fiber precursors. A unique property of polyacrylonitrile is its resistance to chemicals and solvents, which enhances its durability.

PAN is widely used in clothing fabrics, from sweaters to socks, often referred to under the trade name acrylic. It is a lightweight material, which makes it comfortable to wear. Furthermore, because it is less expensive than natural fibers, it is a popular choice for affordable clothing and upholstery.

Monomer Analysis

To understand how polyacrylonitrile is formed, we first need to analyze its monomer structure. The building block of polyacrylonitrile is acrylonitrile, a small organic molecule characterized by its \(\mathrm{CH}_{2} = \mathrm{CHCN}\)This monomer is crucial because it contains:

• A carbon-carbon double bond which enables polymerization.
• A cyano group (\(#N\)) that provides specific chemical properties.

Accurate analysis of the monomers helps in understanding how the entire polymer structure comes into being. The strong interaction between monomers during the polymerization process defines the polymer's characteristics.

Cyano Group

The cyano group, represented by \(#N\), is an essential functional group in organic chemistry. In the structure of acrylonitrile, the cyano group plays a pivotal role in determining the physical and chemical properties of the polymer.

This group consists of a carbon triple-bonded to nitrogen. The presence of the cyano group in acrylonitrile imparts a high degree of polarity to the molecule, affecting how it interacts with other molecules. This aspect significantly contributes to the material's stability and strength, making polyacrylonitrile suitable for high-performance applications.

Polymerization

Polymerization is the process through which monomers are chemically bonded to form a polymer. In the context of polyacrylonitrile, polymerization involves linking multiple acrylonitrile monomers to produce long chains, which contribute to the properties of the resulting material.

There are several types of polymerization, but the most relevant for polyacrylonitrile is addition polymerization. During this process, the double bonds in the acrylonitrile monomer open up, allowing them to connect with other similar units to form a continuous chain:

• Initiation: An initiator activates the acrylonitrile monomer.
• Propagation: The activated monomers link consecutively.
• Termination: The process is stopped once the desired chain length is achieved.

Understanding the polymerization process is crucial for manipulating the molecular weight and properties of the polymer, which eventually determines the application of the material.