Problem 80 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following are condensation polymers? (1) \(\mathrm{PAN}\) (2) Neoprene (3) polystyrene (4) Poly (ethylene terephthalate) (a) 1 and 4 only (b) 3 and 4 only (c) 2 and 3 only (d) 4 only

Step-by-Step Solution

Answer

Option (d) 4 only is the condensation polymer.

Step 1: Understanding Condensation Polymers

Condensation polymers form through a reaction where two or more monomers join together, losing small molecules as by-products, typically water or alcohol. Knowing this is crucial for identifying polymer types.

Step 2: Classifying the Given Polymers

Assess each polymer to identify if it forms through condensation or addition polymerization: 1. Polyacrylonitrile (PAN) - Formed by addition polymerization. 2. Neoprene - Formed by addition polymerization. 3. Polystyrene - Formed by addition polymerization. 4. Poly(ethylene terephthalate) (PET) - Formed by condensation polymerization, involving PTA and EG, releasing water.

Step 3: Selecting Condensation Polymers

Since only Poly(ethylene terephthalate) (PET) forms by condensation polymerization, it alone among the options fits the criteria of a condensation polymer.

Step 4: Choosing the Correct Answer

Based on the analysis, only option (4) is a condensation polymer. Thus, the correct answer is option (d), which corresponds to '(4) only.'

Key Concepts

Polymerization

Polymerization is a chemical process where small units, called monomers, join to form a larger compound known as a polymer. This transformation occurs through different types of reactions, with condensation and addition being two primary methods. In **condensation polymerization**, monomers combine and release a small molecule as a by-product, often water or alcohol. This is a fundamental distinction in identifying polymer types, as not all polymerizations involve by-product release.

In contrast, **addition polymerization** involves the linking of monomers without any by-product formation. Here, monomers typically contain double bonds that open up and link together directly. Recognizing the type of polymerization is vital for understanding the nature and properties of the resulting polymer.

Monomers

Monomers are the building blocks of polymers. These small molecules join together during the polymerization process to create complex structures. Each monomer must have the necessary functional groups to react and form longer chains. In **condensation polymerization**, monomers usually have two functional groups that enable them to connect and release by-products. This makes it possible for these chains to extend and form a polymer
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Conversely, in **addition polymerization**, monomers with double bonds or reactive end groups allow for chain growth without releasing any by-products. Understanding the role of monomers helps in grasping how polymers can have diverse properties depending on the monomers involved and their connectivity.

Poly(ethylene terephthalate)

Poly(ethylene terephthalate), commonly known as PET, is a type of condensation polymer. It is widely used in the manufacturing of fibers and containers due to its strong, durable nature. PET is synthesized through a reaction between two monomers: ethylene glycol (EG) and terephthalic acid (PTA). During its formation, water is released as a by-product.

This by-product formation is indicative of condensation polymerization, which distinguishes PET from other polymers formed through addition processes. PET's robust characteristics and resistance to various chemicals make it a popular material in packaging and textiles.

Addition polymers

Addition polymers are formed through addition polymerization, a process where monomers with unsaturated bonds, typically carbon-carbon double bonds, react to form a polymer without creating any by-products.

Common examples include

• Polyethylene, used in plastic bags.
• Polystyrene, found in foam products.
• Polyacrylonitrile (PAN), utilized in the textile industry.
• Neoprene, used in various elastomer applications.

These polymers are generally used where durability and resistance to chemicals are desired, thanks to their straightforward formation process and strong chemical bonds. Understanding addition polymers helps in differentiating processes that produce majorly man-made materials without significant by-product waste.