Problem 6 - Chemistry in 30 days

Question

Which of the following is a chain-growth polymer ? (a) Orlon (b) Terylene (c) Nylon-6 (d) Glyptal

Step-by-Step Solution

Answer

Orlon is a chain-growth polymer.

Step 1: Define Chain-Growth Polymerization

Chain-growth polymerization is a type of polymerization where the growth of the polymer chain proceeds by successive addition of monomer units with the active site remaining at one end of the growing chain.

Step 2: Analyze the Given Options

Let's analyze each option: - (a) Orlon: This polymer is made through free radical polymerization of acrylonitrile. This is a characteristic of chain-growth polymerization. - (b) Terylene: Known as polyester, it is made through step-growth polymerization from terephthalic acid and ethylene glycol. - (c) Nylon-6: A type of polyamide, manufactured through ring-opening of caprolactam, involving condensation polymerization, not chain-growth. - (d) Glyptal: An alkyd resin, made through step-growth polymerization.

Step 3: Identify the Chain-Growth Polymer

Among the given options, Orlon fits the description of a chain-growth polymer since it is formed by the addition polymerization of acrylonitrile using free radical initiators.

Key Concepts

Polymer Synthesis

Polymer synthesis is a fascinating process central to producing various useful materials. Polymers are long, repeating chains of molecules, and they can be created in different ways. There are two primary types of polymer synthesis: chain-growth polymerization and step-growth polymerization. Each type has its unique mechanism and is suitable for producing different types of polymers.
Chain-growth polymerization involves the addition of monomer units one at a time to an active site, creating a long chain quickly. In contrast, step-growth polymerization typically involves smaller units, or monomers, joining to form larger structures, often requiring heat or other catalysts.

• Understanding these methods helps in synthesizing materials with desired properties.
• Polymer synthesis is crucial in creating plastics, fibers, and other materials used daily.

By employing various techniques, scientists can design polymers with specific characteristics, such as strength, flexibility, and resistance to chemicals.

Addition Polymerization

Addition polymerization, also known as chain-growth polymerization, is a process where monomers add to a growing polymer chain one by one. Each monomer forms a chemical bond, creating a large molecule from simple repeating units. This type of polymerization is essential in creating many common polymers, such as polyvinyl chloride (PVC) and polystyrene.
During addition polymerization, no by-products are formed, making the process straightforward and efficient. This technique is particularly beneficial for producing large quantities of polymer quickly. The mechanism starts with an initiator that creates active sites, leading to the successive addition of monomers to the growing chain.

• Addition polymerization is fast and ideal for producing thermoplastic materials.
• It usually requires specific conditions, such as temperature and pressure, to control the polymer's properties.

Through careful management of these conditions, manufacturers can tailor the properties of the polymer to suit specific applications.

Free Radical Polymerization

Free radical polymerization is a popular form of addition polymerization, known for its ability to create various polymers efficiently. It involves the use of free radicals, which are highly reactive atoms or molecules with unpaired electrons, to initiate the polymerization process. The free radicals react with monomers, creating a reaction chain that contributes to the polymer's growth.
This method is advantageous because it doesn't require metal catalysts, making it easier to handle and safer for some applications. Free radical polymerization is commonly used in creating plastics like polyethylene and polystyrene, among others.

• Free radical polymerization allows for greater control over the molecular weight of the resulting polymer.
• It is versatile, capable of polymerizing a wide variety of monomer types.

Understanding this technique is critical in industries where specific polymer properties are required.

Step-Growth Polymerization

Step-growth polymerization is a distinct type of polymerization that differs significantly from chain-growth processes. In step-growth polymerization, any two monomers or growing chains can react, whereas in chain-growth, the reaction primarily occurs at the active end. This method is commonly used to produce condensation polymers, where small molecules like water or methanol are often released as by-products.
Many traditional synthetic materials, such as nylons and polyesters, are produced using step-growth polymerization. The process generally requires a longer reaction time and often needs heat to drive the reaction to completion.

• Step-growth polymerization is suitable for creating strong, durable materials like fibers and resins.
• It is often slower than chain-growth polymerization but results in materials with excellent mechanical properties.

Understanding both types of polymerizations helps in selecting the right process for designing materials with specific functional attributes.