Branched-chain versus linear polymers: which property is typically lower for branched materials?

Introduction / Context:
Polymer architecture strongly influences packing efficiency, crystallinity, and properties. Branching disrupts chain alignment, which in turn affects density, mechanical strength, and thermal transitions.

Given Data / Assumptions:

• Comparison at similar molecular weights and without heavy fillers.
• Examples: LDPE (branched) vs HDPE (linear).

Concept / Approach:
Branching reduces the ability of chains to pack into crystals, lowering crystallinity. Lower crystallinity typically leads to reductions in density, melting point, and tensile strength compared to linear analogs. Among the listed properties, “density” is a hallmark difference (e.g., LDPE ≈ 0.91–0.93 g/cm^3 vs HDPE ≈ 0.94–0.97 g/cm^3).

Step-by-Step Solution:
Relate branching → reduced packing → reduced crystallinity.Reduced crystallinity → lower density and often lower Tm and tensile strength.Select the most definitive property difference: density.

Verification / Alternative check:
Data sheets for PE grades show clear trends: linear (HDPE) has higher density than branched (LDPE). Similar trends appear in other polymer families when branching increases.

Why Other Options Are Wrong:
Melting point and tensile strength also tend to be lower, but “density” is the most directly and consistently reduced.“None of these” is incorrect since density is affected.

Common Pitfalls:
Attributing differences solely to molecular weight rather than architecture; ignoring branching type (short- vs long-chain branching).

Final Answer:
Density