Problem 3 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following is a chain growth polymer? (a) proteins (b) starch (c) nucleic acid (d) polystyrene

Step-by-Step Solution

Answer

Polystyrene is the chain growth polymer.

Step 1: Understanding Chain-Growth Polymerization

Chain-growth polymerization involves the process of adding monomers with reactive double bonds or other reactive sites one at a time to the growing end of a polymer chain. This is different from step-growth polymerization, where the reaction occurs between all monomers with functional groups. Common examples of chain-growth polymerization include polymerization of alkenes like ethylene to form polyethylene.

Step 2: Analyzing the Options

Examine each option based on the types of monomers and polymerization it involves: - (a) Proteins are formed by amino acids linking through peptide bonds, a step-growth polymerization process. - (b) Starch is a polysaccharide formed by glucose units linked together, another step-growth polymerization example. - (c) Nucleic acids, like DNA and RNA, are formed by nucleotide monomers linking into long chains, also through step-growth polymerization. - (d) Polystyrene is formed by the polymerization of styrene monomers, which involves a chain-growth polymerization process.

Step 3: Determining the Chain-Growth Polymer

Based on the chain-growth polymerization process, the polymers formed from alkenes involve this type of growth mechanism. In the given options, polystyrene is produced from styrene monomers using chain-growth polymerization.

Step 4: Conclusion

Among the given options, polystyrene is the only polymer formed by chain-growth polymerization, with reactive sites in the styrene monomers facilitating a chain addition process.

Key Concepts

polystyrene

Polystyrene is a common plastic used in many everyday items, such as food containers and packaging materials. It is made through a process called chain-growth polymerization, specifically from a monomer known as styrene. The styrene monomers have reactive double bonds, which allow them to connect in a chain-like fashion.
Most notably, polystyrene is a thermoplastic. This means it can be remolded and reshaped when heated, making it very versatile for various applications.

• Characteristics: lightweight, good insulation properties
• Uses: disposable cutlery, building insulation, and more

With its clear and rigid nature, polystyrene is ideal for crafting products that need both flexibility and durability.

step-growth polymerization

Step-growth polymerization is another way polymers are formed. It involves different mechanisms compared to chain-growth polymerization.
In this process, any two molecules containing functional groups can react to form a bond, leading to the creation of a larger molecule. This means that monomers do not need to have reactive double bonds, like those seen in chain-growth polymerization. More often, they have functional groups like -OH or -NH groups. Because of this difference, step-growth polymerization can form both linear and network polymers.

• Examples: Proteins and starch are produced by this method.
• Rate of Reaction: Typically slower than chain-growth polymerization as it requires multiple steps of reactions.

Overall, step-growth polymerization is used for forming complex structures with diverse applications.

polymerization processes

Polymerization processes are chemical reactions where monomers link together to form a polymer. These processes are vital in creating various materials with unique properties, used in countless applications globally.
There are two primary types of polymerization processes: chain-growth and step-growth. Each of these processes has its own characteristics and applications:

• Chain-growth polymerization: Monomers add to the chain one at a time. Commonly involves reactive double bonds.
• Step-growth polymerization: Any two reactive monomers can combine. Requires functional groups such as -COOH or -NH2.

Understanding these processes helps explain why certain materials, like polystyrene, behave the way they do. This knowledge is foundational in fields like material science and chemical engineering.