Animated Solution for Chemistry - Polymers: Which of the following statements about low density polythene is false?

When we think of plastic, polythene is usually the first thing that comes to mind. But not all polythenes are created equal! The world of polymers is fascinating because the macroscopic properties of a material—whether it's soft and squishy or hard and rigid—are entirely dictated by its microscopic molecular structure. In this problem, we are asked to identify the false statement about Low Density Polythene (LDP).

To solve this, we need to understand the fundamental differences between the two main types of polythene: Low Density Polythene (LDP) and High Density Polythene (HDP).

Imagine trying to force thousands of tiny ethene molecules to join hands and form a massive chain. For LDP, this process requires brute force. The synthesis of LDP happens via a free radical addition mechanism.

To get this reaction going, we need extreme conditions: a staggering pressure of $1000$ to $2000\text{ atm}$ and a temperature ranging from $350\text{ K}$ to $570\text{ K}$. Furthermore, the reaction won't just start on its own; it requires a chemical spark. This spark is provided by traces of dioxygen (${\text{O}}_2$) or a peroxide initiator, which act as catalysts to generate the initial free radicals.

Therefore, the statements that its synthesis requires high pressure and a peroxide initiator are absolutely true.

Branching Out

Because LDP is formed through a chaotic free radical mechanism, the resulting polymer chains aren't perfectly straight. They undergo a process called 'chain transfer,' which leads to highly branched structures.

Think of these branched chains like a pile of thorny branches. No matter how hard you try to press them together, the branches get in the way, preventing them from packing tightly. This poor packing results in a lower density—hence the name, Low Density Polythene.

This loose packing makes LDP highly flexible and tough. Like most pure hydrocarbon polymers, it lacks free electrons or ions, making it a very poor conductor of electricity. This makes it an excellent material for insulating electrical wires. So, the statement that it is a poor conductor of electricity is also true.

Because LDP is flexible, it is perfectly suited for making things that need to bend or be squeezed. Squeeze bottles, flexible pipes, and soft plastic toys are classic examples of LDP in action.

But what if you need to make a bucket or a heavy-duty dustbin? If you made a bucket out of LDP, it would be too floppy to hold water effectively! For rigid, sturdy items, we need High Density Polythene (HDP).

HDP is synthesized differently (using a Ziegler-Natta catalyst under mild conditions), resulting in perfectly linear chains with almost no branching. These linear chains pack together tightly like uncooked spaghetti in a box, resulting in a high density, rigid, and hard plastic.

Looking at our options, the statement "It is used in the manufacture of buckets, dustbins etc." is the imposter. Buckets and dustbins require the rigidity of High Density Polythene (HDP), not the flexibility of LDP. Therefore, this is the false statement we were looking for!