Problem 43 - Arihant Objective Approach to Organic Chemistry for IIT JEE and NEET all Medical Entrances Part 4

Question

Which of the following is the example of chain growth polymer? (a) Bakelite (b) Teflon (c) Terylene (d) Nylon-66

Step-by-Step Solution

Answer

Teflon (b) is an example of a chain growth polymer.

Step 1: Understanding Chain Growth Polymerization

Chain growth polymerization involves the linking of monomer units to grow the polymer chain in sequential steps. It starts with an initiation process leading to a reactive center, followed by a chain propagation phase where each monomer added to this center increases the length of the chain.

Step 2: Evaluating Each Option

Let's consider each option: (a) Bakelite is a phenol-formaldehyde resin and is formed via step-growth polymerization. (b) Teflon is formed by polymerizing tetrafluoroethylene through chain growth polymerization. (c) Terylene, a polyester, is formed via step-growth polymerization. (d) Nylon-66 is a polyamide and is synthesized via step-growth polymerization.

Step 3: Selecting the Correct Answer

From the options given, only Teflon fits the description of a polymer formed by chain growth polymerization, as it involves the polymerization of tetrafluoroethylene through the addition of each monomer to a reactive center in a sequential manner.

Key Concepts

Polymerization

Polymerization is the fundamental process responsible for creating polymers by joining smaller molecules called monomers. There are different types of polymerization processes, but one common method is chain growth polymerization. This type of polymerization involves the sequential addition of monomer molecules to a growing polymer chain. The process continues until the monomers are exhausted or another reaction terminates the growth. Characteristics of chain growth polymerization:

• Involves a reactive center that adds one monomer at a time.
• Results in long polymer chains within a relatively short period.
• Often includes an initiation, propagation, and termination stage.

Examples of polymers formed by chain growth polymerization include Teflon and polyethylene. The distinct feature of this method is its ability to rapidly form polymers of high molecular weight.

Initiation Process

The initiation process is the first and crucial step in the chain growth polymerization mechanism. It involves the creation of a reactive center that can attract and add monomer units to the growing polymer chain. Typically, an initiator, such as a free radical or a cation, is used to start this reaction. During the initiation step:

• Free radicals are often generated by thermal decomposition or chemical reactions.
• The reactive center starts interacting with the first monomer, creating the initial bond.
• This leads to the formation of a reactive site on the polymer that can further connect with additional monomers.

The efficiency of the initiation process determines how effectively and quickly the polymerization reaction can begin. Without a successful initiation, the entire polymerization process might fail to proceed.

Monomer Units

Monomer units are the building blocks of polymers. In chain growth polymerization, these small, single-unit molecules join together to form long chains. Each monomer added to the chain contributes to the strength and characteristics of the resulting polymer. Key aspects of monomer units in chain growth polymerization:

• They must be capable of forming a stable bond with the reactive center on the growing polymer chain.
• Different types of monomers can lead to different properties in the final polymer, such as flexibility, durability, or resistance to chemicals.
• The arrangement and type of monomers are crucial for determining the polymer's final application and functionality.

An example is tetrafluoroethylene, the monomer unit of Teflon, known for its non-stick properties and chemical resistance.

Reactive Center

The reactive center in chain growth polymerization is the site where the action happens. It’s where each monomer is added to extend the polymer chain. This center’s main purpose is to provide a location that facilitates the attachment of monomers one at a time, allowing the chain to grow. Important points about the reactive center:

• It is formed during the initiation process and is critical for the propagation of the polymer chain.
• Reactive centers can be radical, ionic, or rarely, a coordination complex, depending on the type of initiator used.
• The nature of the reactive center influences the speed and manner of the polymerization.

In the case of Teflon, the reactive center formed on the initiator enables the continuous addition of tetrafluoroethylene, resulting in the characteristic long polymer chains of Teflon. This ongoing activity at the reactive center is what sustains the chain growth in the polymerization process.