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

Polyethylene glycol is typically formed by anionic polymerization of epoxides, making (c) the correct answer.

Step 1: Understanding the Question

The question asks about the type of polymerization used to produce polyethylene glycol (PEG). Polyethylene glycol is a polymer made from the monomer ethylene glycol or its derivatives, such as epoxides.

Step 2: Identify Key Terms

We need to identify the type of polymerization associated with the production of PEG. The terms include 'free radical polymerization', 'cationic polymerization', and 'anionic polymerization', which are different mechanisms for polymer chain growth.

Step 3: Polymerization of Epoxides

Epoxides, such as ethylene oxide, can undergo polymerization through these mechanisms. Polyethylene glycol is commonly formed using anionic polymerization initiated by a strong base or nucleophile, which opens the epoxide ring.

Step 4: Eliminate Incorrect Options

Free radical polymerization is not typically suitable for epoxides due to their molecular structure. Cationic polymerization can occur but is less common for PEG production compared to anionic polymerization.

Step 5: Determine the Correct Answer

Considering that anionic polymerization is most widely used for producing polyethylene glycol from epoxides, the most accurate choice is option (c), anionic polymerization of epoxider.

Key Concepts

Anionic Polymerization

Anionic polymerization is a method of forming polymers initiated by anions — negatively charged ions. This type of polymerization is particularly significant in the production of polyethylene glycol (PEG). It works effectively on epoxide compounds, such as ethylene oxide, due to their high reactivity with anionic initiators. Anionic polymerizations have the following characteristics:

• They begin with a strong base or a nucleophile which opens the cyclic ethers like epoxide rings.
• The reaction proceeds by the formation and propagation of anionic sites on the growing polymer chain.
• This method allows for controlled molecular weight distribution, which is crucial for achieving specific properties in the final polymer, such as viscosity or melting point.

An advantage of anionic polymerization is its ability to maintain living polymerization conditions, meaning that the polymer chains can continue to grow as long as there are monomers available and no terminating species are introduced. This property is beneficial when precise control of the polymer structure is required.

Epoxide Polymerization

Epoxide polymerization is a chemical process where epoxide monomers, like ethylene oxide, form polymers. This process is key to creating substances like PEG. Epoxides have a three-membered ring structure with oxygen. The strain in this ring makes it highly reactive, ideal for polymerization. For polymerization:

• Epoxide rings are opened by various initiators, in this context, generally anionic in nature.
• These initiators react with the epoxide, leading to chain propagation and subsequently, polymer formation.
• The reaction conditions, such as temperature and solvent type, greatly influence the polymer’s properties.

Epoxide polymerization using anionic mechanisms efficiently helps in synthesizing PEG. This method provides control over polymer architecture, making it suitable for applications where molecular properties must be finely tuned.

PEG Formation

Polyethylene glycol (PEG) formation involves the polymerization of ethylene oxide, a kind of epoxide. PEG is widely used due to its versatile properties and applications, from industrial uses to pharmaceuticals. The formation process typically follows these steps:

• An anionic initiator, often a strong base, starts the polymerization by opening the ethylene oxide rings.
• This initiates a chain reaction where multiple monomers link together, forming long PEG chains.
• The environment during this reaction remains crucial in determining the polymer's characteristics, including its molar mass.

PEGs are known for their excellent biocompatibility, making them suitable for use in medical and cosmetic products. They are also soluble in various solvents, enhancing their versatility in different industrial formulations. This polymerization method allows for precise control over the size and composition of the polymer chains, essential for tailoring PEG for specific applications.