Question

Which of the following is not a semisynthetic polymer? (A) cis-polyisoprene (B) Cellulose nitrate (C) Cellulose acetate (D) Vulcanised rubber

Short answer

The correct answer is \( \boxed{\text{(A) cis-polyisoprene}} \), as it is a natural polymer and has not been chemically modified to create a semisynthetic polymer.

Step-by-step solution

Option A: cis-polyisoprene

Cis-polyisoprene is a natural polymer found in the sap of rubber trees. It has not been chemically modified and, therefore, is not a semisynthetic polymer.

Option B: Cellulose nitrate

Cellulose nitrate is a semisynthetic polymer derived from cellulose, which is a naturally occurring polymer found in the cell walls of plants. Cellulose is chemically modified using nitric acid to produce cellulose nitrate, making it a semisynthetic polymer.

Option C: Cellulose acetate

Cellulose acetate is another semisynthetic polymer derived from cellulose. It is created by modifying cellulose with acetic acid or acetic anhydride, resulting in a semisynthetic polymer.

Option D: Vulcanised rubber

Vulcanised rubber is a chemically modified form of natural rubber (cis-polyisoprene). The process of vulcanization involves the addition of sulfur or other vulcanizing agents to natural rubber, which creates cross-links between the rubber molecules and increases its strength and durability. Consequently, vulcanised rubber is a semisynthetic polymer. From the analysis, we can see that the option that is not a semisynthetic polymer is: \( \boxed{\text{(A) cis-polyisoprene}} \)

Key concepts

cis-polyisoprene

Cis-polyisoprene is a fascinating natural polymer predominantly found in the sap of rubber trees, also known as latex. This naturally occurring material is a fundamental component of natural rubber.

• Structure: It consists of monomer units called isoprene linked together in a specific configuration called the "cis" form.
• Properties: Cis-polyisoprene is renowned for its excellent elasticity, resilience, and water resistance.

The natural, unmodified form of cis-polyisoprene makes it distinct from synthetic or semisynthetic materials. Because it hasn't undergone chemical modification, cis-polyisoprene retains the inherent properties endowed by nature. Understanding cis-polyisoprene is essential in differentiating between natural and semisynthetic polymers, as it serves as a basis for comparison with chemically altered materials.

cellulose nitrate

Cellulose nitrate is a semisynthetic polymer known for its wide range of applications and dynamic properties. Originally derived from cellulose, the backbone of this material comes from natural sources, primarily the cell walls of plants.

Creation and Modification

The process to create cellulose nitrate involves treating cellulose with nitric acid, resulting in the substitution of nitrate groups for some of the hydroxyl groups in the cellulose molecule.

• Transformation: This results in a material that is much more reactive and flammable than its precursor, cellulose.
• Uses: Its flexibility and film-forming properties make cellulose nitrate ideal for uses in lacquers, explosives, and historically, early photography and film materials.

This chemical modification classifies cellulose nitrate as a semisynthetic polymer, highlighting how natural materials can be transformed to meet specific industrial needs.

vulcanised rubber

Vulcanised rubber is a prime example of how simple chemical processes can significantly enhance the properties of a material derived from nature. Originating from natural rubber, or cis-polyisoprene, vulcanisation transforms a naturally elastic material into something with substantially improved characteristics.

The Process of Vulcanisation

Vulcanisation involves adding sulfur or other chemicals to natural rubber, which creates cross-links between polymer chains.

• Benefits: This process increases the strength, resilience, and heat resistance of the polymer, giving it better durability and elasticity.
• Applications: Vulcanised rubber is essential in manufacturing automobile tires, industrial belts, and other materials that require enhanced mechanical properties.

Despite its natural origins, vulcanised rubber is considered semisynthetic because it derives its advanced properties from chemical modifications. This distinction makes it an integral part of industries that rely on durable materials.