Problem 10 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Which of the following statements is not true? [Main Online April 15, \(\mathbf{2 0 1 8}\) (II)] (a) Chain growth polymerisation involves homopoly-merisation only (b) Chain growth polymerisation includes both homo-polymerisation and copolymerisation (c) Nylon 6 is an example of step-growth polymerisation (d) Step growth polymerisation requires a bifunctional monomer

Step-by-Step Solution

Answer

Statement (a) is not true.

Step 1: Understanding Polymerization

Polymerization is the process of reacting monomer molecules together to form polymer chains. There are two main types of polymerization: chain-growth and step-growth. Chain-growth polymerization involves the growth of polymer chains from active sites, while step-growth polymerization involves stepwise reactions between bi-functional or multi-functional monomers.

Step 2: Analyzing Chain-Growth Polymerization

In chain-growth polymerization, polymer chains grow by the successive addition of monomer units to an active site. This type of polymerization can involve both homopolymerization, where only one type of monomer is used, and copolymerization, where two or more different monomers are used.

Step 3: Analyzing Step-Growth Polymerization

Step-growth polymerization involves reactions between monomers with two or more functional groups. Nylon 6 is created through a step-growth process as it is synthesized from a single monomer, caprolactam, which undergoes ring-opening polymerization, a step-growth process despite involving a single component.

Step 4: Identifying the Incorrect Statement

Statement (a) claims that chain-growth polymerization involves only homopolymerization, which is not true since it can also involve copolymerization. Therefore, statement (a) is incorrect.

Key Concepts

Chain-Growth Polymerization

Chain-growth polymerization is a fascinating process that creates polymer chains by adding one monomer unit at a time. Think of it like adding beads to a necklace, where each bead represents a monomer. This process happens at active sites on the growing polymer chain, which can be thought of as the clasp to which new beads are added.
As the chain grows, there are two main variations:

• Homopolymerization: Involves the use of a single type of monomer. Imagine all the beads being the same color.
• Copolymerization: Here, two or more types of monomers are used, creating a pattern of beads in different colors. This allows the creation of polymers with properties tailored by the ratios and arrangement of the different monomers.

In contrast to step-growth polymerization, chain-growth occurs quickly and can produce high molecular weight polymers even at low conversions.

Step-Growth Polymerization

Step-growth polymerization unfolds differently from chain-growth polymerization. Here, the polymer forms through a series of reactions between multi-functional monomers.
Each monomer has functional groups that allow them to bond with others, creating larger molecules step by step. This process doesn't focus on a single active site but rather involves all monomers reacting with each other as they come into contact. Because of this, step-growth polymerization doesn’t necessarily require a rapid addition of monomer units, and high molecular weights are achieved only near the end of the reaction when most monomers have reacted.

• Nylon 6 is an excellent example, synthesized through a step-growth reaction involving caprolactam.
• It's worth noting that each step in the polymerization contributes to the overall molecular structure, making this method particularly valuable in creating strong, high-performance materials.

Homopolymerization

In homopolymerization, a single type of monomer is used throughout the polymerization process. Imagine a repetitive sequence of identical letters forming a very long word.
This kind of polymerization results in polymers with uniform properties, as all the monomer units are the same. Some notable properties of homopolymers include consistent melting points and mechanical stability, which are often desirable in applications requiring uniform performance.

• Homopolymerization is common in chain-growth polymerizations, but it can appear in step-growth scenarios as well, particularly if only one functional group type is involved.

Understanding homopolymerization helps in controlling the characteristics of the polymer, making it a fundamental concept in polymer chemistry.

Copolymerization

Copolymerization introduces complexity and versatility to the process of polymer formation by allowing different monomer types to join in constructing the polymer chain. Much like mixing different ingredients in a recipe, this method results in a material with varied properties depending on the nature and proportions of the monomers.
There are several forms of copolymerization:

• Random copolymerization: Monomers are incorporated randomly into the polymer chain.
• Block copolymerization: Large sequences of the same monomer repeat, followed by sequences of another monomer.
• Alternating copolymerization: Monomers alternate in a regular pattern along the polymer chain.

By carefully selecting monomers and their arrangement, scientists can design polymers for specific uses, enhancing characteristics like flexibility, durability, or thermal resistance.