Problem 69 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following pairs is not correctly matched? (a) Teflon: Thermally stable cross linked polymer of phenol and formaldehyde (b) Synthetic rubber: A copolymer of butadiene and styrene (c) Terylene: Condensation polymer of terephthalic acid and ethylene glycol (d) Perspex: A homopolymer of methyl methacrylate

Step-by-Step Solution

Answer

Option (a) is not correctly matched.

Step 1: Analyze the Options

Read each option to understand what each substance is said to be and match with its description or chemical nature.

Step 2: Evaluate Option A

Option a) describes Teflon as a thermally stable cross-linked polymer of phenol and formaldehyde. However, Teflon is actually a polymer of tetrafluoroethylene and is not related to phenol and formaldehyde, which are associated with Bakelite.

Step 3: Evaluate Option B

Check if the description of synthetic rubber is correct. A copolymer of butadiene and styrene is commonly known as SBR (Styrene-Butadiene Rubber), a correct description for synthetic rubber.

Step 4: Evaluate Option C

Terylene is indeed a condensation polymer, and terephthalic acid with ethylene glycol forms polyethylene terephthalate, which is correct as per this description.

Step 5: Evaluate Option D

Perspex is described as a homopolymer of methyl methacrylate, which is accurate as it is a common name for polymethyl methacrylate (PMMA), used as a lightweight, shatter-resistant alternative to glass.

Key Concepts

Teflon

Teflon, widely known for its non-stick properties, is not what some people might assume. It is not a cross-linked polymer of phenol and formaldehyde as described in the original exercise. Instead, Teflon is made from a monomer called tetrafluoroethylene. This unique polymer is characterized by its ability to withstand high temperatures and resist chemical reactions.

• Tetrafluoroethylene polymerizes to form long chains of carbon atoms surrounded by fluorine atoms.
• These fluorine atoms provide the non-stick and heat-resistant properties Teflon is famous for.

Teflon’s applications range from cookware coatings to industrial uses. Its stability and low friction make it ideal for scenarios where surfaces need to move slippage-free over each other without adhering.

Synthetic Rubber

While natural rubber comes from latex found in rubber trees, synthetic rubber is manufactured through chemical processes. One common type of synthetic rubber is Styrene-Butadiene Rubber, or SBR. This copolymer is made from two monomers: butadiene and styrene.

• Butadiene contributes flexibility and elasticity to the resulting rubber.
• Styrene adds strength and helps the rubber maintain its shape while still being flexible.

SBR is often used in automobile tires due to its durability and cost-effectiveness. It's also used in shoe soles, conveyor belts, and many other products where resilient rubber is required. The ability to tailor the proportions of butadiene and styrene allows manufacturers to tweak the properties of SBR for specific applications.

Condensation Polymers

Unlike polymers that form by adding identical units together, condensation polymers result from a different process. They form through a reaction where two different types of monomers join together, typically releasing a small molecule like water as a byproduct. Terylene, for example, is a well-known condensation polymer.

• Terylene is created from the monomers terephthalic acid and ethylene glycol.
• The polymerization reaction yields water, illustrating the term "condensation" polymerization.

Such polymers are prominent in the textile industry, offering advantages like durability and resistance to wrinkling. Other well-known condensation polymers include nylon and polyester, which are used in everything from clothing to industrial materials.

Homopolymers

Homopolymers are composed of a single type of monomer repeatedly bonded together. This is in contrast to copolymers, which use two or more different monomers. A great example of a homopolymer is Perspex, also known as polymethyl methacrylate (PMMA).

• Each recurring unit in PMMA is derived from the monomer methyl methacrylate.
• Because of its clarity and lightweight nature, PMMA is often used as a glass alternative.

This specific characteristic makes it valuable in applications such as lenses, aquariums, and protective barriers. Homopolymers like PMMA demonstrate that even a single type of monomer can create materials with versatile and useful properties.