Understanding Polymer Classification: Natural, Semisynthetic, and Synthetic

Polymers are large molecules made up of repeating structural units called monomers. They can be classified based on their origin into three main types:

• Natural Polymers: These are found in nature, such as proteins, nucleic acids, starch, cellulose, and natural rubber (cis-polyisoprene).
• Semisynthetic Polymers: These are derived from natural polymers by chemical modification. Examples include cellulose derivatives like cellulose nitrate and cellulose acetate, and vulcanised rubber. These polymers possess properties improved compared to their natural counterparts.
• Synthetic Polymers: These are completely synthesized in the laboratory from simple monomers. Examples include polyethylene, nylon, PVC, etc.

The question asks to identify the option that is not a semisynthetic polymer. Let's examine each option provided to determine its classification.

Analysing the Given Options to Identify Semisynthetic Polymer Types

We need to go through each option and classify it as natural, semisynthetic polymer, or synthetic.

1. cis-polyisoprene: This is the chemical name for natural rubber. Natural rubber is obtained from the latex of rubber trees and is a prime example of a natural polymer. It is not a semisynthetic polymer as it is not a chemically modified version of another natural polymer.
2. Cellulose nitrate: This polymer is prepared by treating cellulose (a natural polymer) with nitric acid. This chemical modification of natural cellulose results in a semisynthetic polymer. It was historically used as guncotton and celluloid.
3. Cellulose acetate: This polymer is also prepared by chemically modifying cellulose (a natural polymer), typically by acetylation. Cellulose acetate is a well-known semisynthetic polymer used in fibres (like rayon before), films, and plastics. Its properties are different from natural cellulose due to the introduction of acetate groups.
4. Vulcanised rubber: Natural rubber (cis-polyisoprene) itself has limitations like being soft, sticky, and having low tensile strength. Vulcanisation is a process where natural rubber is heated with sulfur to improve its properties, making it harder, stronger, and more elastic. Since it is a chemical modification of a natural polymer (natural rubber), vulcanised rubber is considered a semisynthetic polymer.

Conclusion: Identifying What is Not a Semisynthetic Polymer

Based on the analysis of each option:

• cis-polyisoprene is a natural polymer.
• Cellulose nitrate is a semisynthetic polymer.
• Cellulose acetate is a semisynthetic polymer.
• Vulcanised rubber is a semisynthetic polymer.

Therefore, cis-polyisoprene is the only option among the choices that is not a semisynthetic polymer. It is a natural polymer.