Question

Which one of the following is not an example of chain growth polymer? (a) neoprene (b) Buna-S (c) PMMA (d) glyptal

Short answer

Glyptal (d) is not a chain growth polymer.

Step-by-step solution

Understanding Chain Growth Polymers

Chain growth polymers, also known as addition polymers, are formed by the polymerization of monomers that possess double or triple bonds, such as alkenes or alkynes. In chain growth polymerization, the process requires an initiator to start a chain reaction where monomers add sequentially to a growing chain.

Identifying the Given Polymers

Let's analyze each option to identify their polymerization process: - Neoprene is a polymer of chloroprene, formed by the chain growth mechanism. - Buna-S is a copolymer made from styrene and butadiene, also formed via chain growth. - PMMA (Poly(methyl methacrylate)) is synthesized through chain growth polymerization from methyl methacrylate monomers. - Glyptal is a type of alkyd resin, formed from the reaction of glycerol and phthalic anhydride, utilizing a step-growth polymerization process.

Identifying the Odd Polymer: Glyptal

Glyptal, unlike the first three examples, is a condensation polymer formed by step growth polymerization rather than chain growth polymerization. It primarily involves the condensation of monomers leading to small molecule by-products like water or methanol during polymer formation.

Conclusion

From the analysis and the basics of polymerization processes, it becomes clear that Glyptal is the polymer formed by a different process (step growth polymerization), distinguishing it from the chain growth polymers listed.

Key concepts

addition polymers

Addition polymers, commonly referred to as chain growth polymers, are constructed by the linking of monomers with unsaturated bonds, such as alkenes, that allow the creation of long polymer chains. This type of polymerization involves three main stages: initiation, propagation, and termination.

• **Initiation**: An initiator, often a radical, opens the double or triple bonds of a monomer to start the chain reaction.
• Propagation: The opened bond allows monomers to add onto the growing chain sequentially, forming long macromolecules.
• Termination: Eventually, the growing chains stop expanding when the chain end on one polymer meets another or when another molecule acts to stop the reaction.

This process is distinct in that it primarily adds monomers without the loss of any small molecules. Examples like polystyrene and polyethylene are quintessential addition polymers.

step-growth polymerization

Step-growth polymerization is a different approach to forming polymers that involves the stepwise reaction between monomers containing two or more functional groups. This mode of polymerization is typical for creating polymers like polyesters and polyamides. Different from chain growth, step-growth polymerization includes the following features:

• **Polymer Growth**: It doesn't require any initiators, and monomers react with each other at various points, not needing a sequential chain reaction.
• **Heterogeneous Reaction**: Unlike chain growth, where each reaction adds one monomer at a time, step-growth reactions tend to involve the combination of oligomers – small chains that grow by the combination of two reative ends.
• **By-products Formation**: Smaller molecules, such as water or alcohol, are often lost during the formation of polymers, which is a defining characteristic of this method.

The polymerization of monomers through successive reaction steps allows flexibility in forming complex polymer structures.

polymerization processes

Polymerization processes are fundamental chemical reactions in which small molecules, known as monomers, are transformed into large macromolecules called polymers. These processes can be complex, and they are broadly classified into two main types: addition polymerization and step-growth polymerization.
**Addition Polymerization** involves monomers with unsaturated bonds linking without the loss of small molecules, as seen in polyethylene and polystyrene manufacture.
**Step-Growth Polymerization** involves monomers with complementary functional groups reacting to form polymers, often with the loss of small by-products like water.
In these processes, consideration of factors like the reactivity of monomers, types of bonds involved, and the need for catalysts or initiators can greatly influence the overall structure and properties of the resulting polymer, affecting everything from strength to flexibility.

condensation polymer

Condensation polymers are a common type of step-growth polymer formed by reactions that produce small molecules as by-products. This formation usually involves monomers with two functional groups which condensate to form polymer chains. Key features of condensation polymers include:

• **Formation of By-products**: Typically, small molecules such as water or alcohol are expelled during the polymer-forming processes.
• **Examples**: Polyesters, such as polyethylene terephthalate (PET), and polyamides, like nylon, are made through condensation polymerization.
• **Chain Growth through Reaction**: Unlike addition polymers, which use an initiator, condensation polymers grow through the reaction of monomer ends.

These polymers are widely used due to their customizable properties, supporting diverse applications such as in textiles, packaging, and engineering components due to their strength and durability.