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Chapter 12: Problem 92

What molecular structural features cause high-density polyethylene to be denser than low-density polyethylene?

Short Answer

Expert verified
The key molecular structural feature causing high-density polyethylene (HDPE) to be denser than low-density polyethylene (LDPE) is the linearity of its polymer chains. HDPE has a more linear, less branched structure, allowing chains to pack closely together, whereas the greater amount of branching in LDPE leads to a less organized, more random arrangement of chains, resulting in a lower density material.

Step by step solution

01

Understand the molecular structure of polyethylene

Both HDPE and LDPE are made from the same monomer, ethylene (C2H4). The difference in their densities comes from the way these monomers are polymerized, resulting in different molecular structures. Polymerization is the process where ethylene monomers are connected to form long polymer chains.
02

Identify the differences in molecular structures

HDPE has a more linear molecular structure with fewer branches compared to LDPE, which has a more branched molecular structure. Linear molecules pack more tightly together, whereas the presence of branches in LDPE prevents the chains from packing as closely.
03

Understand the impact of molecular structure on density

In HDPE, the linear structure allows the chains to pack closely together, leading to a higher density. In contrast, the greater amount of branching in LDPE results in a less organized and more random arrangement of polymer chains, leading to a lower density material. So, the main molecular structural feature that causes high-density polyethylene to be denser than low-density polyethylene is the linearity of its polymer chains compared to the more branched structure of LDPE chains.

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Most popular questions from this chapter

The first LEDs were made from GaAs, which has a band gap of $1.43 \mathrm{eV}$. What wavelength of light would be emitted from an LED made from GaAs? What region of the electromagnetic spectrum does this light correspond to: ultraviolet, visible, or infrared?

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