Problem 116 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is a polyamide? [2005] (a) Teflon (b) Nylon-6, 6 (c) Terylene (d) Bakelite

Step-by-Step Solution

Answer

Nylon-6, 6 is a polyamide.

Step 1: Understanding Polyamides

Polyamides are polymers where the repeating units are linked by amide bonds. To identify which option is a polyamide, we need to look for a polymer made by reacting compounds with amide (–CONH–) linkages.

Step 2: Identify the Structure of Each Option

Let's start by identifying what each option is made of: (a) Teflon - Made of tetrafluoroethylene, it is not a polyamide but a polyfluorinated polymer. (b) Nylon-6, 6 - Formed by condensation polymerization of hexamethylenediamine and adipic acid, forming amide linkages. (c) Terylene - A polyester formed from ethylene glycol and terephthalic acid, not an amide. (d) Bakelite - Made by polymerization of phenol and formaldehyde, it is a phenolic resin, not a polyamide.

Step 3: Analyzing the Options for Amide Linkages

From the above analysis: Teflon and Terylene are excluded for being a polyfluorinated compound and a polyester respectively, which don't use amide linkages. Bakelite is a phenolic resin and also doesn't have amide linkages. Nylon-6, 6, however, is made through reactions that form amide linkages.

Step 4: Reaffirm the Characteristics of Polyamides

Polyamides are generally characterized by the presence of recurring amide bonds in their structure. Nylon-6, 6, specifically, is named for these linkages and is well-known for them.

Step 5: Select the Correct Option

With the understanding that Nylon-6, 6 has the necessary amide linkages indicative of a polyamide, we conclude it must be the correct answer.

Key Concepts

Nylon-6, 6

Nylon-6, 6 is a type of synthetic polymer known as a polyamide, which is a crucial material in various applications due to its robust properties. Its name comes from the two monomers it is synthesized from:

• Hexamethylenediamine
• Adipic acid

Both monomers contain six carbon atoms, which explains the '6, 6' in its name. The creation of Nylon-6, 6 involves a reaction called condensation polymerization. This process results in the formation of long chains where each repeating unit is linked by an amide bond, giving Nylon-6, 6 its high strength and elasticity.

• High tensile strength
• Good elasticity
• Excellent resistance to abrasion

These properties make it ideal for applications like textiles, automotive parts, and equipment requiring durability.

Amide Linkages

Amide linkages are the bonds that join the monomers in polyamides, such as Nylon-6, 6. They form through a chemical reaction between a carboxylic acid group (\[-COOH\]) and an amine group (\[-NH_2\]). During this reaction, water (\[H_2O\]) is released as a byproduct. Known as an amide bond or peptide bond, this linkage is denoted by the structure:

\[-CONH-\] This bond is crucial to the structure and properties of polyamides. Amide linkages provide strength and stability to the polymer chains, making materials like Nylon-6, 6 tough and durable.

• Robust bond holding the polymer chain together
• Creates a repeating pattern in the polymer
• Contributes to high melting point and strength

The repeating amide linkages are what give polyamides their unique characteristics, which are essential for their widespread usage.

Polymerization

Polymerization is a chemical process that combines small molecules called monomers into a larger compound known as a polymer. In the case of Nylon-6, 6, this process is specifically known as condensation polymerization.

During this process, monomers with carboxylic acid and amine groups react together, releasing a small molecule, usually water, each time a bond forms. For Nylon-6, 6, this means each time an amide linkage is formed, a water molecule is expelled.

Some traits of polymers like Nylon-6, 6 that result from polymerization include:

• High thermal stability
• Flexibility in application
• Ability to be formed into fibers

This process makes polyamides valuable in manufacturing and industrial applications. Thanks to polymerization, we can produce fibers and materials with specific traits tailored to meet the demands of different industries.