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 \(\mathrm{nA}+\mathrm{nB} \rightarrow-\mathrm{B}-\mathrm{B}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{B}-\mathrm{B}\) \(-\mathrm{B}-\mathrm{B}-\mathrm{B}-\mathrm{B}-\mathrm{A}-\mathrm{A}-\) (a) Alternate copolymer (b) Block copolymer (c) Graft copolymer (d) Random copolymer

Step-by-Step Solution

Answer

The given polymer is a block copolymer.

Step 1: Define Types of Copolymers

To answer the question, we first need to understand the types of copolymers. Alternate copolymers have monomers arranged in a regular alternating sequence. Block copolymers have large blocks of each type of monomer. Graft copolymers have a main chain of one type of monomer with branches of different types. Random copolymers have a random distribution of monomers.

Step 2: Examine the Polymer Structure

The given polymer structure is \(-\mathrm{B}-\mathrm{B}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{B}-\mathrm{B}-\) followed by \(-\mathrm{B}-\mathrm{B}-\mathrm{B}-\mathrm{B}-\mathrm{A}-\mathrm{A}-\). Here, the \(-\mathrm{A}-\) units and \(-\mathrm{B}-\) units are arranged in large blocks, showing areas where one monomer type predominates before switching to the other.

Step 3: Determine the Type of Copolymer

Given the arrangement of the monomers, with large sequences of \(-\mathrm{A}-\) followed by large sequences of \(-\mathrm{B}-\), this pattern is indicative of a block copolymer.

Key Concepts

Polymerization

Polymerization is a chemical process essential to forming polymers, which are large molecules composed of repeated subunits called monomers. This transformation involves connecting numerous monomer units through covalent chemical bonds. This results in long chains or networks. Polymerization can occur through different mechanisms, each defined by how the monomers are linked together. The process is broadly divided into two main types:

• Addition Polymerization: Monomers add to each other without the loss of any small molecules. This mechanism is common in producing many commercial plastics.
• Condensation Polymerization: This involves the combination of monomers with the simultaneous elimination of a small molecule such as water or methanol. It is often seen in forming polyesters or nylons.

Each type of polymerization yields materials with varying properties, pivotal in different applications, ranging from plastics to synthetic fibers and rubbers.

Monomers

Monomers are the fundamental building blocks of polymers. These small molecular units can be linked together in various sequences to create a broad range of polymer structures. The unique characteristics of monomers define the specific properties of the resultant polymer, such as strength, flexibility, and resistance to chemicals.

• Types of Monomers: Monomers are categorized based on their chemical nature and functional groups. Common examples include ethylene, propylene, and styrene.
• Functionality: A vital characteristic of monomers is their functionality, i.e., the number of bonding sites available. This determines the complexity and type of polymer that can be formed.

The diversity of monomers enables creating a wide variety of polymers, tailored for specific purposes, from everyday household items to specialized engineering materials.

Block Copolymer

Block copolymers are a unique class of copolymers where blocks of one type of monomer repeat unit are connected to blocks of another type. This structure allows the combination of different characteristics from each block, providing multifunctional properties in a single material. The architecture of block copolymers can be tailored for specific applications, leading to innovations in materials science.

• Structure: They consist of two or more distinct polymer blocks linked together, with each block consisting of a large number of identical monomer units. The distinct regions in block copolymers often result in the material exhibiting properties of both parent polymer types.
• Applications: These materials are often used in creating nanostructured materials, drug delivery systems, and as adhesives or coatings due to their ability to self-organize into well-defined structures.

The ability to modify the block segments' length and composition allows for extensive customization of mechanical and thermal properties, enhancing their usefulness across different industries.

Types of Copolymers

Copolymers are polymers formed by polymerizing two or more different monomer species. The specific arrangement of these monomers within the polymer chain defines the type of copolymer. There are several key types:

• Alternate Copolymers: In these copolymers, the monomer units alternate in a regular pattern, forming a highly ordered sequence. This can result in enhanced material properties like toughness and clarity.
• Block Copolymers: As previously discussed, these feature long sequences of each monomer type grouped in blocks, allowing the combination of differing physical properties.
• Random Copolymers: Here, the monomers are arranged without any specific order, leading to a more amorphous and flexible polymer structure.
• Graft Copolymers: These have a backbone of one type of monomer with branches (grafts) of another. Such structures are beneficial in applications requiring specific surface properties or enhanced compatibility between phases.

Understanding the different types of copolymers and their configurations helps in selecting the right material for desired applications, whether for enhancing performance or creating new functional materials.