Problem 1 - A Complete Resource Book in Chemistry for JEE Main

Question

Polymer formation from monomers starts by (a) condensation reaction between monomers (b) coordination reaction between monomers (c) conversion of monomer to monomer ions by protons (d) hydrolysis of monomers

Step-by-Step Solution

Answer

Polymer formation starts by a condensation reaction between monomers.

Step 1: Identify Polymerization Type

Polymerization is a process in which small monomer molecules join to form a long polymer chain. This can occur through various reactions, predominantly addition (chain-growth) and condensation (step-growth) polymerization. In this question, we need to determine the initial reaction responsible for polymer formation.

Step 2: Understand Condensation Reaction

In condensation polymerization, monomers join through a reaction that releases a small molecule, such as water or alcohol. This process often involves bifunctional or polyfunctional reagents, where each monomer has at least two reactive ends to facilitate chain-building.

Step 3: Evaluate Other Reactions

Examining other options, hydrolysis is the breakdown of compounds by water, which does not contribute to polymer formation. Coordination reactions relate to catalysts forming complexes to control polymer reactions, often used in coordination polymerization rather than directly starting polymerization. The conversion of monomers to ions is typically involved in ionic polymerization, which isn't explicitly indicated here.

Step 4: Match Reaction to Polymerization

Condensation reactions effectively form polymers by consistently linking monomer units while releasing small molecules like water or alcohol. Hence, condensation fits the scenario of initial polymer formation if the monomers engage in this through their reactive ends.

Key Concepts

Condensation Reaction

Understanding a condensation reaction is crucial in the realm of polymer chemistry. In a condensation reaction, monomers come together to form a larger molecule, and as a byproduct, a small molecule like water, methanol, or hydrogen chloride is released. These reactions typically involve monomers that have at least two functional groups.
This is why they are sometimes referred to as step-growth polymerizations.
Condensation reactions are characterized by:

• Monomers bearing reactive functional groups such as hydroxyl or carboxyl groups.
• The release of small molecules as the reaction proceeds.
• Commonly used in producing polyesters and polyamides.

As these monomers react, they form long chains of polymers, linking together through the consecutive release of small units.

Monomers

Monomers are the fundamental building blocks of polymers. These small molecules join together in repeating sequences to form larger structures known as polymers.
Monomers need specific reactive sites to enable them to polymerize effectively.
Common characteristics of monomers include:

• Small molecular size.
• Presence of reactive functional groups that allow bonding between molecules.
• Capability to form various types of polymers based on their structure.

Understanding how monomers behave and interact is crucial as they define the properties of the resulting polymer, such as flexibility, durability, and thermal resistance.

Addition Polymerization

Addition polymerization is a process where monomers combine without the loss of any small molecules. This is different from condensation polymerization.
Only the breakage of double bonds or ring structures occurs for monomers to chain together.
The key points about addition polymerization include:

• Monomers have unsaturated bonds, typically carbon-carbon double bonds, which open up during the reaction.
• No byproducts are formed, which distinguishes this method from other polymerization techniques.
• This process is commonly used to create everyday plastics, such as polyethylene and polypropylene.

The formation is typically rapid, making it a valuable method for producing versatile materials with a wide range of applications.

Ionic Polymerization

Ionic polymerization is a unique type of polymerization driven by ionic species initiating and propagating the reaction. There are two main variations: cationic and anionic polymerization.
Each uses ionic catalysts to create polymers.

• Cationic polymerization uses positively charged species to start the reaction, suitable for certain vinyl and diene polymers.
• Anionic polymerization involves negatively charged species and is ideal for producing polymers such as polybutadiene and styrene.

This method offers precise control of polymer structures, making it indispensable when producing polymers with specific properties and high uniformity.