Problem 94 - A Complete Resource Book in Chemistry for JEE Main

Question

Poly ethylene glycol is farmed as a result of? (a) free radical polymerisation of epoxider (b) cationic polymerisation of epoxider (c) anionic polymerisation of epoxider (d) Can be any of these

Step-by-Step Solution

Answer

c) anionic polymerisation of epoxider

Step 1: Understanding the Question

The question is asking about the polymerization method used to synthesize polyethylene glycol (PEG). This involves determining which type of polymerization process is commonly used to produce PEG.

Step 2: Identify Polymerization Types

Review the three given polymerization types: free radical, cationic, and anionic polymerization, each of which represents different chemical reactions based on the charged species involved or radicals in the process.

Step 3: Recognize the Correct Process

Polyethylene glycol is typically produced through the anionic polymerization of ethylene oxide, a type of epoxide. In this process, an anionic initiator attacks ethylene oxide, causing polymerization.

Step 4: Analyze Other Options

Consider why the other two options (free radical and cationic polymerization) are less commonly associated with the production of PEG. These methods are typically used for different monomers than ethylene oxide.

Key Concepts

Anionic Polymerization

Anionic polymerization is a fascinating process that significantly contributes to the synthesis of polyethylene glycol (PEG). It involves the use of anions, which are negatively charged ions, as initiators. In simpler terms, think of it as using negatively charged particles to start a chain reaction. One of the most common initiators in this process includes compounds like alkali metals.
In anionic polymerization, the initiator first attacks the monomer, creating an active center. The new center continues to react with additional monomer molecules, chaining them together. This chain reaction leads to the formation of long polymer chains, which are essentially the building blocks of plastics like PEG.

• Highly efficient and precise: Because of the nature of anions, this process provides excellent control over the length and structure of the polymer chain.
• Living polymerization: Once initiated, the reaction continues as long as there are available monomers, allowing for more controlled and predictable results.
• Minimal termination: Unlike other polymerization processes, there is minimal chance of the chain reaction stopping prematurely.

This method's precision and control make it particularly suitable for creating PEG, which needs to have consistent properties for its various applications.

Polymerization Processes

Polymerization refers to the process of combining many small molecules known as monomers into a covalently bonded chain or network. It plays a crucial role in creating various plastics and polymers, including polyethylene glycol. Various polymerization processes exist, each with distinct characteristics and suitable applications.
When discussing polymerization processes, we typically consider:

• Free Radical Polymerization - In this method, radicals (atoms with unpaired electrons) initiate the reaction. It's often used in creating polystyrene and polymethyl methacrylate.
• Cationic Polymerization - Here, positively charged ions initiate the reaction. This method is suitable for producing polymers like butyl rubber.
• Anionic Polymerization - As described earlier, this utilizes negatively charged ions for initiation and is the method employed in PEG production.

Each process uses different initiators and mechanisms to create chains of varying lengths and structures. The choice of process largely depends on the desired properties of the final polymer.

Ethylene Oxide

Ethylene oxide is a crucial component in the production of polyethylene glycol. It is a type of epoxide, which makes it a versatile monomer because of its ability to open its three-membered ring structure during reactions. This ability is particularly important in polymerization processes such as anionic polymerization.
During the synthesis of PEG, ethylene oxide reacts with an anionic initiator. This initial reaction opens the strained ring of the ethylene oxide, allowing further addition of more ethylene oxide molecules. Essentially, this chain continues to grow as long as there are available ethylene oxide monomers and no termination event stops the process.
Key properties of ethylene oxide:

• Highly reactive: The strained ring structure makes it very reactive, thus a perfect candidate for polymerization.
• Versatile: Suitable for both anionic and cationic polymerization, offering broad applications in different chemical processes.
• Precise control: Its use in processes like anionic polymerization offers significant control over the molecular weight and structure of the resulting polymer.

Ethylene oxide's role is pivotal in ensuring the successful synthesis of PEG, impacting the efficiency and properties of the resulting polymer.