Thermosetting polymer, bakelite is formed by the reaction of phenol with
(a) CH3CH2CHO
(b) CH3CHO
(c

Q: Why is Bakelite called a thermosetting polymer?

Bakelite is called a thermosetting polymer because during its formation, extensive covalent cross-links are created between the polymer chains. Once these bonds are formed and the plastic 'sets' into a shape, it cannot be melted or reshaped by heating. Heating it further will only cause it to burn or degrade.

Q: What is the difference between Novolac and Bakelite?

Novolac is a linear polymer formed in the initial stages of the reaction between phenol and formaldehyde (usually with an excess of phenol). It is thermoplastic. Bakelite is formed when Novolac is further heated with more formaldehyde, causing it to cross-link into a rigid, infusible 3D network, making it thermosetting.

Q: Why does formaldehyde react specifically at the ortho and para positions of phenol?

The $-OH$ group on the phenol ring is an electron-donating group through resonance. It increases the electron density of the benzene ring, particularly at the ortho and para positions. Therefore, the electrophile generated from formaldehyde preferentially attacks these electron-rich sites.

Q: What type of polymerization forms Bakelite?

Bakelite is formed via condensation polymerization (also known as step-growth polymerization). This is because the joining of the monomer units involves the elimination of small molecules, specifically water ($H_2O$), during the formation of the methylene bridges.

Q: Can I use acetaldehyde ($CH_3CHO$) instead of formaldehyde to make Bakelite?

No. Formaldehyde ($HCHO$) is unique because it has two reactive sites (the two hydrogen atoms can be replaced) allowing it to form a $-CH_2-$ bridge between two phenol rings. Acetaldehyde has a bulky methyl group which would cause steric hindrance and prevent the dense cross-linking required to form the rigid Bakelite structure.

Question

Thermosetting polymer, bakelite is formed by the reaction of phenol with

Options:

(A) $CH_3CH_2CHO$

(B) $CH_3CHO$

(C) HCHO

(D) HCOOH

Sigma Percentile · Accepted Answer

### The Birth of the First Synthetic Plastic

Imagine a world without plastics. Hard to do, right? The journey of modern plastics began with a remarkable material called **Bakelite**. Invented by Leo Baekeland in 1907, Bakelite was the world's first fully synthetic plastic. But what exactly is it made of, and why is it so special? Let's dive into the fascinating chemistry behind this revolutionary material.

### The Building Blocks: Phenol and Formaldehyde

To build a massive polymer structure, we need small, reactive building blocks called monomers. For Bakelite, nature provides us with two relatively simple molecules:

1.  **Phenol** ($C_6H_5OH$): An aromatic ring with a hydroxyl group attached. The hydroxyl group makes the benzene ring highly reactive, specifically at the *ortho* and *para* positions.
2.  **Formaldehyde** ($HCHO$): The simplest aldehyde. It acts as the perfect 'bridge-builder' in our chemical construction site.

When phenol and formaldehyde are mixed in the presence of an acid or base catalyst, a condensation reaction kicks off.

### From Linear Chains to a 3D Fortress

Initially, the reaction forms ortho- and para-hydroxymethyl phenols. These intermediate molecules then react with each other, eliminating water molecules (hence the term *condensation* polymer), to form a linear polymer chain known as **Novolac**. Novolac is often used in paints and varnishes.

But the magic happens when we want to make something truly indestructible.

If we take Novolac and heat it with an excess of formaldehyde ($HCHO$), the formaldehyde molecules form $-CH_2-$ (methylene) bridges between the linear Novolac chains. This process is called **cross-linking**.

### The Power of Thermosetting

The result of this extensive cross-linking is a massive, interconnected three-dimensional network. Because the chains are now locked together by strong covalent bonds, the material becomes incredibly rigid and heat-resistant.

This is the defining characteristic of a **thermosetting polymer**. Unlike thermoplastics (like the polythene used in plastic bags), which can be melted and reshaped repeatedly, a thermosetting polymer like Bakelite is permanently set once it is formed. If you try to heat it again, it won't melt; it will simply char and degrade.

Therefore, knowing that Bakelite is a phenol-formaldehyde resin, the correct reactant that pairs with phenol is undoubtedly formaldehyde, represented by the chemical formula **$HCHO$**.

Animated Solution for Chemistry - Organic Chemistry: Thermosetting polymer, bakelite is formed by the reaction of phenol with

Select Answer:

Visualized Solution

$Identifying the Polymer$

$Monomers of Bakelite$

$The Polymerization Process$

$Conclusion$

The Sigma Insight: Polymers

The Birth of the First Synthetic Plastic

The Building Blocks

From Linear Chains to a 3D Fortress

The Power of Thermosetting

Similar Questions

Preparation of bakelite proceeds via reactions

The polymer formed on heating novolac with formaldehyde is

The formation of which of the following polymers involves hydrolysis reaction?

Which one of the following polymers is not obtained by condensation polymerisation?

Which statement is correct?

Which polymer is used in the manufacture of paints and lacquers?

Among the following, the correct statement(s) about polymers is(are)

The two monomers for the synthesis of nylon 6, 6 are

On complete hydrogenation, natural rubber produces

Which of the following compounds is a constituent of the polymer $— HN — C ∣∣ O — NH — CH_{2} —_{n}$ ?