Animated Solution for Chemistry - Organic Chemistry: The correct match between Item-I and Item-II is $\begin{array}{ll}\text{Item-I}& \text{Item-II}\\ \text{A. High density polythene}& \text{I. Peroxide catalyst}\\ \text{B. Polyacrylonitrile}& \text{II. Condensation at high temperature and pressure}\\ \text{C. Novolac}& \text{III. Ziegler-Natta catalyst}\\ \text{D. Nylon-6}& \text{IV. Acid or base catalyst}\end{array}$

Imagine you are a chemical engineer tasked with synthesizing various polymers. You have a list of desired polymers on one side and a toolkit of catalysts and reaction conditions on the other. Our goal is to perfectly match each polymer to its specific manufacturing requirement. This isn't just about memorization; it's about understanding the fundamental mechanism behind each polymerization process.

Let's start with High Density Polythene (HDPE). When we want to create HDPE, we need the polymer chains to pack closely together. This means we absolutely cannot have branching in our carbon chains.

To achieve this perfectly linear structure, we use a specialized coordination catalyst known as the Ziegler-Natta catalyst, which is typically a mixture of titanium tetrachloride (${\text{TiCl}}_4$) and triethylaluminium (${\text{Al(C}}_2{\text{H}}_5{)}_3$). This catalyst guides the ethylene monomers to attach in a strictly linear fashion. Therefore, High Density Polythene (A) pairs perfectly with the Ziegler-Natta catalyst (III).

Next up is Polyacrylonitrile (PAN), a synthetic resin used to make acrylic fibers. PAN is formed through the addition polymerization of acrylonitrile monomers.

This specific addition reaction proceeds via a free radical mechanism. To kickstart a free radical chain reaction, we need an initiator that easily breaks apart to form radicals. A peroxide catalyst is the perfect candidate for this job. Thus, Polyacrylonitrile (B) matches with the Peroxide catalyst (I).

The Phenol-Formaldehyde Resin

Moving on to Novolac, which is a linear condensation polymer formed from the reaction between phenol and formaldehyde.

This reaction is a classic example of electrophilic aromatic substitution followed by condensation. To facilitate this, the reaction medium must be either acidic or basic to activate the formaldehyde or the phenol, respectively. Hence, Novolac (C) requires an Acid or base catalyst (IV).

Ring-Opening Polymerization

Finally, we have Nylon-6. Unlike Nylon-6,6 which is made from two different monomers, Nylon-6 is synthesized from a single monomer called caprolactam, which is a cyclic amide.

To polymerize caprolactam, we must break its stable ring structure. This ring-opening polymerization is achieved by heating the caprolactam with water at a high temperature (around 533 K) and high pressure. This process hydrolyzes the ring into an amino acid, which then undergoes continuous condensation. Therefore, Nylon-6 (D) matches with Condensation at high temperature and pressure (II).

Bringing it all together, our logical deduction gives us the sequence: A $\to$ III, B $\to$ I, C $\to$ IV, D $\to$ II. This perfectly aligns with option (a).

Always remember, the choice of catalyst or reaction condition doesn't just speed up the reaction; it fundamentally dictates the physical properties and the very identity of the resulting polymer!