Problem 106 - A Complete Resource Book in Chemistry for JEE Main

Question

Polymer is a very large molecule that is made up of repeating small molecular units called monomers. The chemical reaction that unites the monomers is called polymerization. There are homopolymers, copolymers depending upon the type of monomers present in them. Following is the example of \(\mathrm{nA}+\mathrm{nB} \rightarrow-\mathrm{B}-\mathrm{B}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{B}-\mathrm{B}\) \(-B-B-B-B-A-A-\) (a) Alternate copolymer (b) Block copolymer (c) Graft copolymer (d) Random copolymer

Step-by-Step Solution

Answer

The polymer is a block copolymer.

Step 1: Understand the Definition of Polymers

A polymer is a large molecule made by linking many smaller molecules called monomers. When similar monomers link, they form a homopolymer, and when different monomers unite, they form a copolymer. Each copolymer has a specific structure depending on the arrangement of monomers.

Step 2: Analyze the Provided Example

The given polymer example is a combination of two types of monomers, A and B, linked together, depicted as \(-\mathrm{B}-\mathrm{B}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{B}-\mathrm{B}\). This type of sequence suggests a specific pattern in the arrangement of monomers.

Step 3: Recognize the Block Copolymer Structure

In a block copolymer, large continuous sequences of one type of monomer are followed by sequences of another type. Observing the polymer, we see blocks of A (\(-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\)) and blocks of B (\(-\mathrm{B}-\mathrm{B}-\)). Thus, this pattern indicates a block copolymer.

Step 4: Identify the Correct Type of Copolymer

Given the specific arrangement of monomers in the polymer (-BB-AAAAAA-BB-), where blocks of each type of monomer are present, this corresponds to the definition of a block copolymer. Therefore, the correct choice is (b) block copolymer.

Key Concepts

Polymerization

Polymerization is a transformative chemical reaction essential for the creation of polymers. In simple terms, it's the process where small molecules, called monomers, join together to form a larger and more complex structure known as a polymer. This process can be thought of as stringing together beads to form a necklace.

There are two main categories of polymerization:

• Addition Polymerization: In this type, monomers add together without the loss of any small molecules. It's a straightforward process mostly involving unsaturated monomers that have double bonds.
• Condensation Polymerization: In this method, each time monomers join, a small molecule (like water) is released. This is often seen in the creation of bio-polymers like proteins.

Understanding polymerization is crucial because it determines the type and characteristics of the resulting polymer, influencing its physical and chemical properties.

Monomers

Monomers are the building blocks of polymers, much like single bricks used to build a wall. These small molecules are the basic repeating units that attach in various patterns to create the diverse structures of polymers.

Monomers can be:

• Simple: Composed of a single chemical unit that repeats.
• Complex: Made from larger and more intricate chemical structures.

For example, in polyethylene, ethylene monomers (C₂H₄) repeat to form a long chain polymer. When you mix different kinds of monomers, you get copolymers with unique properties. This capability to combine different monomers allows the creation of materials with tailored functionalities for specific applications.

Copolymer Structure

Copolymers result from polymerizing two or more distinct types of monomers. The sequence and pattern of these monomers determine the specific copolymer structure, affecting its properties and uses. There are four primary types of copolymer structures:

• Block Copolymer: Contains long sequences or "blocks" of each type of monomer. These blocks create materials with zones of differing physical properties, often leading to unique applications in both science and industry.
• Alternating Copolymer: Monomers alternate in a regular pattern (e.g., -ABABAB-). This regularity offers a unique set of mechanical and thermal properties.
• Graft Copolymer: Chains of one type of monomer are "grafted" onto a backbone made of another type, producing materials with specialized properties.
• Random Copolymer: Monomers are arranged randomly along the chain. This randomness creates materials with a balance of properties from the constituent monomers.

The arrangement and type of monomers in a copolymer significantly impact its function and application, ranging from synthetic fabrics to pharmaceuticals.