Problem 10 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

Among the following polymers, identify the homopolymer (a) Bakelite (b) Dacron (c) Natural rubber (d) Orlon

Step-by-Step Solution

Answer

Natural rubber and Orlon are homopolymers.

Step 1: Define Homopolymer

A homopolymer is a polymer that is formed from a single type of monomer unit. This means every repeating unit in a homopolymer is identical.

Step 2: Analyze Bakelite

Bakelite is a thermosetting plastic formed from the polymerization of phenol and formaldehyde. Since it involves two different types of monomers, it is not a homopolymer.

Step 3: Analyze Dacron

Dacron, also known as polyethylene terephthalate (PET), is formed from the condensation polymerization of ethylene glycol and terephthalic acid, involving two different monomers. Therefore, it is not a homopolymer.

Step 4: Analyze Natural Rubber

Natural rubber is polymerized from isoprene units (2-methyl-1,3-butadiene). Since it is composed of repeating units of the same monomer, it qualifies as a homopolymer.

Step 5: Analyze Orlon

Orlon is a trade name for a kind of polyacrylonitrile polymer. It is made from the polymerization of acrylonitrile monomers, a single type of monomer, making it a homopolymer as well.

Key Concepts

Homopolymer

In organic chemistry, a homopolymer is a type of polymer that is composed entirely of one kind of monomer. Let's break down the term: "homo-" means "same" or "one" in Greek, signifying that all the repeating units in the polymer are identical.
This singularity in composition gives homopolymers a uniform structure, which can influence their physical properties like melting point and tensile strength. For example, **natural rubber** is a homopolymer because it's formed from the polymerization of isoprene units.

• Each molecule of natural rubber is composed exclusively of isoprene, a single monomer type.
• This consistent structure makes it uniquely elastic and resilient.

Homopolymers are essential in various applications, from rubber bands to everyday plastic utensils, showcasing their versatility.

Polymers

Polymers are large molecules made by chemically bonding many smaller units called monomers. The term "polymer" comes from the Greek words "poly," meaning many, and "meros," meaning parts.
This makes polymers essentially giant chains (or networks) of repeated sub-units. They are classified into several types based on their composition and properties: homopolymers and copolymers.

• **Homopolymers**: Made from identical monomers, as seen in natural rubber or Orlon.
• **Copolymers**: Consist of two or more different monomers, like Bakelite and Dacron, which use phenol and formaldehyde, and ethylene glycol and terephthalic acid, respectively.

Polymers play critical roles in daily life, providing materials that range from flexible to rigid, transparent to opaque, and used in everything from clothing to industrial components.

Polymerization

The process of linking monomers into polymers is called polymerization. This can occur through several mechanisms, primarily categorized as addition polymerization and condensation polymerization.
Each type has unique characteristics and applications.

• **Addition Polymerization**: Involves the successive addition of monomers with unsaturated bonds, like the formation of Orlon from acrylonitrile.
• **Condensation Polymerization**: Typically involves the removal of small molecules (like water) during the chemical bonding of the monomers, as seen in the formation of Dacron.

These processes allow the creation of diverse polymer types, each with distinct properties tailored for specific purposes, from clothing to engineering applications.

Monomers

Monomers are small, basic molecular units that can join together to form polymers. These building blocks are unified through chemical reactions to form the large, complex structures we know as polymers.
A single type of monomer linked together forms a homopolymer, while different types create copolymers. For example,

• In natural rubber, **isoprene** is the monomer that repeats to create its chain-like structure.
• In Dacron, the monomers **ethylene glycol and terephthalic acid** react to form long polymer chains through condensation polymerization.

Understanding monomers is crucial because their nature determines the polymer's properties and potential applications, influencing everything from softness to durability, flexibility to strength.