Problem 5 - A Complete Resource Book in Chemistry for JEE Main

Question

Low density polythene is prepared by (a) free radical polymerization (b) cationic polymerization (c) anionic polymerization (d) Ziegler-Natta polymerization

Step-by-Step Solution

Answer

Low density polythene is prepared by free radical polymerization.

Step 1: Identifying the Polymerization Method

Low density polythene (LDPE) is a type of polyethylene characterized by its branched polymer structure and is typically produced through a process that involves the use of specific catalysts or conditions. In this question, we need to identify which polymerization method is used for its production.

Step 2: Analyzing Free Radical Polymerization

Free radical polymerization is a process that utilizes free radicals to initiate the polymerization of monomers. This method is often used for producing polymers with a branched structure due to the nature of side reactions that can occur during polymerization. branched structure is typical for LDPE.

Step 3: Examining Other Polymerization Methods

Cationic and anionic polymerizations are ion-based and typically involve different mechanisms, leading often to polymers with linear structures rather than branched. Ziegler-Natta polymerization is typically used for high-density polythene and results in a linear polymer chain.

Step 4: Choosing the Correct Answer

Given the need for a branched structure in LDPE, free radical polymerization is the appropriate method of choice, as it promotes the formation of branches during polymerization, unlike the other methods listed.

Key Concepts

Free Radical Polymerization

Free radical polymerization is a fascinating chemical process used to form polymers by linking monomers together through their free radicals. Free radicals are molecules that possess an unpaired electron, making them highly reactive. This process begins with an initiation step, where an initiator creates free radicals that react with a monomer, starting the chain reaction. This results in the formation of long polymer chains.

This method is particularly useful for producing polymers with branched structures. During the polymerization, side reactions can occur, leading to the formation of branches. This branching is critical for certain types of polymers, such as low-density polyethylene (LDPE). The branching affects the polymer’s density, flexibility, and strength.

• Initiation: Generates the initial free radicals to kick-start the reaction.
• Propagation: Monomers successively add to form a long chain.
• Termination: The reaction concludes, ending the growth of the polymer chain.

Free radical polymerization is often used for commercial applications where a less dense and more flexible material is desired.

Low Density Polyethylene (LDPE)

Low Density Polyethylene (LDPE) is a versatile plastic known for its resilience and flexibility. It is produced using free radical polymerization, a process that encourages branching of the polymer chains. This branching results in a lower density compared to other forms of polyethylene like High Density Polyethylene (HDPE).

LDPE's branched structure offers several advantages:

• It creates a more flexible material.
• Enhances toughness and makes the plastic less prone to breaking.
• Results in a product that resists chemical attack from various substances.

These properties make LDPE perfect for use in products like shopping bags, containers, and flexible bottles. Its lightweight nature makes it highly desirable for applications where ease of handling and transportation are essential. LDPE remains a popular choice in many industries due to its adaptability and economic advantages.

Polymer Structure Analysis

Understanding the structure of polymers is crucial in determining their properties and applications. Polymer structure analysis involves examining the arrangement of the polymers’ molecular chains. In the case of LDPE, the focus is on its branched structure resulting from free radical polymerization.

LDPE’s branching occurs due to: - The presence of side chains emanating from the main polymer chain. - Irregularities in the chain growth due to free radical processes.

• Branched Structure: Creates spaces within the material, leading to lower density.
• Chain Mobility: Allows for greater flexibility.
• Intermolecular Forces: Weaker than those in linear polymers, resulting in unique properties like softness.

Analyzing these elements helps chemists and material scientists adjust polymerization conditions to tailor polymers for specific needs. It is through such analysis that innovations in material design continue to evolve, leading to better and more efficient industrial and consumer applications.