Question

The polyethylene with minimum number of branches is

• A. LDPE
• B. HDPE
• C. LLDPE
• D. VLDPE

Hint:

Less branching in polyethylene leads to higher density and tensile strength.

Answer 1

The Correct Option is B

Step 1: Understanding polyethylene structures.
Polyethylene types differ mainly in the degree of branching in their polymer chains. Branching affects density, strength, and crystallinity.
Step 2: Branching comparison.
HDPE (High-Density Polyethylene) has very little branching, allowing polymer chains to pack closely. This results in higher density and strength compared to other types.
Step 3: Analysis of options.
(A) LDPE: Highly branched structure.
(B) HDPE: Correct — Has the least branching.
(C) LLDPE: Has short-chain branching.
(D) VLDPE: More branching than HDPE.
Step 4: Conclusion.
HDPE has the minimum number of branches, hence option (B) is correct.

Answer 2

Branching in polyethylene and its resulting density are directly linked: fewer branches allow chains to pack tighter, giving higher density, so ranking density is one way to rank branching.

1. LDPE: Made by high-pressure free-radical polymerization, which favours both short-chain and long-chain branching through intramolecular and intermolecular chain transfer (back-biting) reactions. This gives it the most branching of the group and the lowest density among these options.
2. HDPE: Made using coordination catalysts (Ziegler-Natta or Phillips-type) under low pressure, which produce an almost perfectly linear chain with very few branch points. Fewer branches let the chains pack closely into a highly crystalline structure, giving HDPE its characteristic high density and rigidity.
3. LLDPE: Made by copolymerizing ethylene with a small amount of an alpha-olefin comonomer (like butene or hexene) using coordination catalysts, which deliberately introduces short, uniform side-chain branches along an otherwise linear backbone - more branching than HDPE, but less than LDPE.
4. VLDPE: Made similarly to LLDPE but with a higher proportion of comonomer, giving it even more short-chain branching than LLDPE and correspondingly lower density and crystallinity.

Ranking by branching from least to most: HDPE < LLDPE < VLDPE < LDPE, which makes HDPE the one with the minimum number of branches.

Therefore, the correct answer is HDPE.