Monomer of novolac is
(a) 3-hydroxybutanoic acid
(b) phenol and melamine
(c) o-hydroxymethylphenol
(

Q: Why doesn't p-hydroxymethylphenol form Novolac?

While p-hydroxymethylphenol is formed during the reaction, the linear polymer Novolac is primarily formed by the condensation of o-hydroxymethylphenol. Cross-linking involving the para position leads to the formation of Bakelite.

Q: Is Novolac a thermoplastic or thermosetting polymer?

Novolac itself is a thermoplastic polymer. However, upon further heating with formaldehyde, it undergoes cross-linking to form Bakelite, which is a thermosetting polymer.

Q: What type of polymerization forms Novolac?

Novolac is formed through condensation polymerization, where water molecules are eliminated as byproducts during the linkage of monomer units.

Q: Can we use any other aldehyde instead of formaldehyde?

Formaldehyde is specifically used because its high reactivity and small size allow it to easily form methylene bridges (-CH2-) between phenol rings without steric hindrance.

Q: Why is an acid or base catalyst required?

The catalyst facilitates the formation of the reactive electrophile (in acidic medium) or increases the nucleophilicity of phenol (in basic medium), thereby speeding up the initial electrophilic aromatic substitution.

Question

Monomer of novolac is

Options:

(A) 3-hydroxybutanoic acid

(B) phenol and melamine

(C) o-hydroxymethylphenol

(D) 1,3-butadiene and styrene

Sigma Percentile · Accepted Answer

### The World of Polymers

Welcome to the fascinating world of polymers! When we look around, from the plastics we use daily to the complex proteins in our bodies, polymers are everywhere. In the realm of synthetic polymers, **phenol-formaldehyde resins** hold a special place of historical and industrial significance.

Today, we are going to unravel the mystery behind one such important polymer: **Novolac**. The question asks us to identify the monomer of Novolac. To do this, we need to trace its chemical origins.

### The Birth of Novolac

Imagine a reaction flask where we mix **phenol** and **formaldehyde**. When we add a little bit of acid or base as a catalyst, a beautiful chemical dance begins. This reaction is a classic example of **electrophilic aromatic substitution**.

The formaldehyde molecule, acting as an electrophile, attacks the electron-rich ortho and para positions of the phenol ring. This initial attack doesn't immediately give us a giant polymer. Instead, it forms intermediate compounds known as hydroxymethyl phenols.

$$ 	ext{Phenol} + 	ext{Formaldehyde} \xrightarrow{	ext{H}^+ 	ext{ or OH}^-} o	ext{-hydroxymethylphenol} + p	ext{-hydroxymethylphenol} $$

### Identifying the Monomer

Now, here is where the story of Novolac specifically takes shape. Novolac is known to be a **linear polymer**. For a polymer chain to grow linearly without branching out into a complex 3D web, the polymerization must primarily proceed through one specific type of linkage.

In the case of Novolac, the linear chain is formed by the continuous condensation of the ortho-substituted product. The molecules link together, eliminating water molecules in the process, to form methylene bridges ($-CH_2-$) between the phenol rings.

Therefore, the fundamental building block—the monomer—that repeats to form this linear chain is **$o$-hydroxymethylphenol**.

### The Final Verdict

Looking at our options, we can easily spot our hero. Option (c) is exactly what we derived: $o$-hydroxymethylphenol.

**Correct Option: (c)**

*Bonus Insight:* If you were to take this linear Novolac and heat it with even more formaldehyde, it would undergo extensive cross-linking, utilizing the para positions as well. This transforms the thermoplastic Novolac into a rigid, infusible, thermosetting plastic known as **Bakelite**. Always keep this bigger picture in mind!

Animated Solution for Chemistry - Organic Chemistry: Monomer of novolac is

Select Answer:

Visualized Solution

$Origin of Novolac$

$Electrophilic Substitution$

$The Monomer Unit$

$Structure Analysis$

$Conclusion$

$Beyond Novolac$

The Sigma Insight: Polymers

The World of Polymers

The Birth of Novolac

Identifying the Monomer

The Final Verdict

Similar Questions

The polymer formed on heating novolac with formaldehyde is

Which among the following is not a polyester ?

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

The homopolymer formed from 4-hydroxybutanoic acid is

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

Monomer units of dacron polymer are

Orlon fibres are made up of

Which of the following polymer is used in the manufacture of wood laminates?

Buna-N synthetic rubber is a copolymer of

Poly- $β$ -hydroxybutyrate-Co- $β$ -hydroxyvalerate (PHBV) is a copolymer of ......