Introduction to Polymers - SS3 Chemistry Lesson Note
Polymers are large molecules composed of repeating structural units called monomers. These macromolecules play a significant role in modern materials science, chemistry, and everyday life. The study of polymers is a crucial branch of science known as polymer chemistry or macromolecular chemistry. Polymers can be found in various forms, ranging from natural biopolymers like proteins and DNA to synthetic polymers used in plastics, fibres, and coatings. Let's delve into an advanced introduction to polymers:
Classification of Polymers:
Polymers can be classified based on their source, structure, and synthesis:
a. Based on Source:
● Natural Polymers: These are found in nature and are often derived from biological sources. Examples include proteins, DNA, cellulose, starch, and rubber.
● Synthetic Polymers: These are human-made and can be further divided into two categories:
● Addition Polymers: Formed through the polymerization of monomers with double bonds, such as polyethene and polypropylene.
● Condensation Polymers: Result from the reaction of monomers with two or more functional groups, releasing small molecules as byproducts, such as nylon and polyester.
b. Based on Structure:
● Linear Polymers: Have a linear chain structure without any branches, such as polyethene - Branched Polymers: Contain side branches along the main chain, which affect their properties and processing behaviour.
● Crosslinked Polymers: Form a three-dimensional network through covalent bonds, leading to a more rigid and insoluble material, like vulcanised rubber.
c. Based on Synthesis:
● Addition Polymerization: Involves the direct linking of monomers without the elimination of any byproducts, as seen in the polymerization of ethylene to form polyethene.
● Condensation Polymerization: Requires the elimination of small molecules like water or alcohol as byproducts during the polymerization process, as seen in the formation of nylon and polyester.
Polymerization Reactions:
Polymerization is the process of linking monomers together to form a polymer chain. It can occur through different methods:
a. Addition Polymerization: Occurs through a chain reaction initiated by radicals, ions, or metal catalysts. Monomers with unsaturated double bonds (e.g., ethylene, styrene) undergo repeated addition reactions to form polymers.
b. Condensation Polymerization: Involves monomers with two or more functional groups (e.g., carboxyl and amino groups). The reaction produces a small molecule (e.g., water or alcohol) as a byproduct during the polymerization process.
Properties and Applications:
Polymers exhibit a wide range of properties and have diverse applications in various industries:
a. Mechanical Properties: Polymers can be flexible, elastic, or rigid, depending on their structure and cross-linking. This makes them suitable for use in various products, such as plastics, rubbers, and fibres.
b. Thermal Properties: Polymers can have varying melting and glass transition temperatures, which affect their processing and application in different temperature conditions.
c. Electrical Properties: Some polymers are excellent insulators, while others can conduct electricity, making them useful in electronic and electrical applications.
d. Biodegradability: Some polymers, particularly certain biopolymers and certain synthetic polymers, are biodegradable, making them environmentally friendly.
e. Applications: Polymers are used in countless applications, including packaging materials, textiles, medical devices, automotive components, adhesives, and coatings.
Polymer Structure-Property Relationships:
The structure of a polymer, including its molecular weight, branching, and crosslinking, significantly influences its properties and behaviour. Structure-property relationships are essential for tailoring polymers to specific applications.
In summary, polymers are versatile and essential materials with diverse structures and properties. Their wide range of applications and ability to be tailored for specific purposes make them indispensable in modern life and technology. The study of polymers continues to advance, leading to the development of new materials with improved properties and increased sustainability.