Question

Low-density polyethylene (LDPE) has a higher degree of chain branching than highdensity polyethylene (HDPE). Explain the relationship between chain branching and density.

Short answer

Answer: Chain branching affects the density of LDPE and HDPE by influencing how closely the polymer chains can pack together. The higher degree of chain branching in LDPE causes the polymer chains to be more irregular, which makes it difficult for the chains to pack closely together, resulting in a lower density. In contrast, HDPE has less chain branching, allowing the chains to have a more linear structure and pack together more efficiently, leading to a higher density.

Step-by-step solution

Understanding the Structure of LDPE and HDPE

Low-density polyethylene (LDPE) and high-density polyethylene (HDPE) are both polymers made from the same monomer, ethylene (C2H4). They mainly differ in their structure, where LDPE has a higher degree of chain branching compared to HDPE. Chain branching refers to the presence of side chains on the primary polymer chain. In the case of LDPE, the branches are irregular and randomly distributed.

Explaining the Concept of Density

Density is defined as the mass per unit volume of a substance. In the context of polymers, higher density means that the polymer chains are more closely packed together, which affects their physical properties such as tensile strength, rigidity, and resistance to heat and chemicals.

Comparing Density of LDPE and HDPE

The primary difference between LDPE and HDPE lies in their density. As the name suggests, low-density polyethylene (LDPE) has a lower density compared to high-density polyethylene (HDPE). The density of LDPE is typically in the range of 0.910 to 0.925 g/cm³, while the density of HDPE varies between 0.941 and 0.965 g/cm³.

Explaining the Relationship between Chain Branching and Density

The higher degree of chain branching in LDPE causes the polymer chains to be more irregular, which makes it difficult for the chains to pack closely together. As a result, the density of LDPE is lower than that of HDPE, where the chains have a more linear structure and can pack together more efficiently. The lower density in LDPE leads to different physical properties such as flexibility and transparency, whereas HDPE's higher density gives it greater strength, rigidity, and resistance to heat and chemicals.