Question

Identify the correct statement with respect to high-density polythene

• A. TiCl$_4$ and Et$_3$Al used as catalyst for preparation
• B. Obtained by polymerization at 350–570 K
• C. Has highly branched structure
• D. Chemically active

Hint:

HDPE Characteristics.

• Catalyst used: Ziegler–Natta (TiCl$_4$ + Et$_3$Al).
• Low branching: Leads to high crystallinity and density.
• Uses: Pipes, containers, toys, due to rigidity and chemical resistance.

Answer 1

The Correct Option is A

High-Density Polyethylene (HDPE) is formed by polymerization of ethene using a Ziegler–Natta catalyst system. Let’s evaluate each option:

• Option (1): TiCl$_4$ (titanium tetrachloride) and Et$_3$Al (triethylaluminum) are components of the Ziegler–Natta catalyst system. This is correct.
• Option (2): Polymerization at 350–570 K corresponds to low-density polyethylene (LDPE), which is prepared using free-radical polymerization. HDPE is prepared at lower temperatures, around 333–343 K. Incorrect.
• Option (3): HDPE has a linear structure with minimal branching, contributing to its high density. Incorrect.
• Option (4): HDPE is chemically inert and widely used for containers, piping, etc. Incorrect.

Hence, option (1) is correct.

Answer 2

Step 1: Understanding High-Density Polyethylene (HDPE)
High-density polyethylene (HDPE) is a type of polyethylene characterized by its linear structure with minimal branching, which results in a dense, strong, and crystalline polymer.

Step 2: Catalyst used in HDPE preparation
HDPE is commonly prepared by the polymerization of ethylene using specific catalysts that control the polymer structure. One of the widely used catalysts for HDPE production is a combination of titanium tetrachloride (TiCl₄) and triethylaluminum (Et₃Al). This catalyst system is part of the Ziegler-Natta catalyst family.

Step 3: Role of TiCl₄ and Et₃Al
TiCl₄ acts as the active metal component, while Et₃Al serves as a co-catalyst that activates TiCl₄ by reducing it to a lower oxidation state, facilitating the polymerization process to produce HDPE with high density and crystallinity.

Step 4: Conclusion
Therefore, the correct statement is that TiCl₄ and Et₃Al are used as catalysts for the preparation of high-density polyethylene.