Question

Which of the following is a condensation polymer? (a) Polyacrylonitrile (b) Bakelite (c) Glyptal (d) Nylon \(-6,6\)

Short answer

Bakelite, Glyptal, and Nylon ,6 are condensation polymers; option (d) is specifically asked.

Step-by-step solution

Identify Condensation Polymer

Condensation polymers are formed through a step-growth polymerization process where monomers react to form a polymer and a small molecule, such as water or methanol, is lost during the formation. We need to identify which of the given options is formed by this process.

Analysis of Options

Let's analyze each option to determine if it is a condensation polymer: (a) Polyacrylonitrile - This polymer is formed by addition polymerization, not condensation, hence it is not a condensation polymer. (b) Bakelite - This polymer is formed by the condensation of phenol with formaldehyde and eliminates water molecules during the polymerization process, so it is a condensation polymer. (c) Glyptal - It is formed by the polycondensation of a dibasic acid (phthalic anhydride) and a dihydric alcohol (ethylene glycol), releasing water. (d) Nylon ,6 - This polymer is formed by the condensation of hexamethylenediamine and adipic acid, releasing water molecules during the process.

Conclusion and Selection

Options (b), (c), and (d) are all condensation polymers as they all release small molecules during their formation. Among these, Nylon ,6 is a well-known example out of the options given.

Key concepts

Step-Growth Polymerization

Step-growth polymerization is a critical process in the formation of many useful polymers. Unlike chain-growth polymerization, where monomers add to a growing chain one at a time, step-growth polymerization involves the reaction of bifunctional or multifunctional monomers. In this process, each monomer has two or more reactive groups. Each of these reactive groups can connect with similar groups on other monomers. This kind of polymerization happens in steps, gradually building larger chain molecules. It's important to note that any two units can combine at any time, resulting in a wide range of potential connections as the reaction proceeds.
Overall, step-growth polymerization is characterized by:

• The involvement of monomers with multiple functional groups.
• The possibility of forming oligomers, which are shorter polymer chains, before they link into a larger structure.
• The creation of complex macromolecules even in the initial stages.

Examples of polymers formed through step-growth polymerization include polyesters, polyamides, and phenol-formaldehyde resins.

Polymerization Process

The polymerization process is at the heart of creating materials with a variety of applications, ranging from plastics to fibers. In the context of condensation polymers, the polymerization process is typically a step-growth process. During this process, monomers with reactive functional groups combine step-wise, forming increasingly long polymer chains.
This process usually consists of several stages:

• Initiation, where reactive monomers come together to form dimers or small oligomers.
• Propagation, as these oligomers join together to create longer chains.
• Termination, resulting in the final polymer structure.

Condensation polymerization is unique because, during each step, a small molecule—often water—is released as a byproduct. This release accompanies the joining of monomer units, leading to long-lasting, stable polymers.

Monomers React

In condensation polymerization, monomers react with one another to form polymer chains. This reaction occurs because these monomers have specific reactive groups. When these reactive groups are brought close together, often through heating or the use of catalysts, they can form covalent bonds with each other.
For instance:

• In Bakelite formation, phenol and formaldehyde react, where hydroxyl and aldehyde groups interact to form a complex polymer network.
• In the production of Glyptal, a dicarboxylic acid (phthalic anhydride) reacts with a diol (ethylene glycol), again through ester linkages.
• Nylon (-6,6 ) formation involves the reaction of a diacid (adipic acid) with a diamine (hexamethylenediamine), forming strong amide bonds.

The type of monomers and their functional groups determine both the structure and properties of the resultant polymer.

Small Molecule Release

One of the hallmarks of condensation polymerization is the release of small molecules, which most commonly include water or methanol. This release is critical because it represents the formation of new covalent bonds between monomer units, leading to the growth of the polymer chain.
For every bond formed during polymerization, a small molecule is released. This side product must be carefully managed as it affects the efficiency and environment of the polymerization process. Small molecule release can often necessitate specific conditions—such as temperature, pressure, and catalysts—to ensure that the polymer forms correctly and with the desired properties.
Understanding the release of small molecules is essential in engineering and chemistry, as it not only signifies the progress of the polymerization but also can affect the purity and physical characteristics of the final polymer product.