Classification of Polymers - SS3 Chemistry Lesson Note
Polymers are classified based on various factors, including their source, structure, and properties. Understanding the classification of polymers is essential in identifying and categorising the diverse range of macromolecules used in various industries. Let's explore the classification of polymers in detail:
Based on Source:
a. Natural Polymers: These polymers are derived from natural sources and are often found in biological systems. They are produced by living organisms through biosynthesis. Examples of natural polymers include:
● Proteins: Such as collagen, keratin, and enzymes.
● Nucleic Acids: DNA and RNA, which carry genetic information.
● Carbohydrates: Including cellulose, starch, and chitin.
● Natural Rubber: Derived from the latex of rubber trees.
b. Synthetic Polymers: These polymers are human-made through chemical synthesis. They can be further categorised into addition polymers and condensation polymers, based on their polymerization process.
● Addition Polymers: Formed through the polymerization of monomers with unsaturated double bonds, without the elimination of any byproducts. Examples include polyethene, polypropylene, and polyvinyl chloride (PVC).
● Condensation Polymers: Result from the reaction of monomers with two or more functional groups, leading to the elimination of small molecules (e.g., water or alcohol) as byproducts. Examples include nylon, polyester, and polyurethane.
Based on Structure:
a. Linear Polymers: These polymers have a simple linear chain structure without any branches or crosslinks. Examples include high-density polyethene (HDPE) and polyvinyl chloride (PVC).
b. Branched Polymers: Branched polymers have side chains branching out from the main chain. The presence of branches affects the polymer's properties and processing behaviour. Examples include low-density polyethene (LDPE) and some elastomers.
c. Crosslinked Polymers: Crosslinked polymers form a three-dimensional network structure due to covalent bonds between polymer chains. This cross-linking makes the material more rigid and insoluble. Examples include vulcanised rubber and some thermosetting plastics.
Based on Polymerization Mechanism:
a. Addition Polymers: These polymers are formed by the addition of monomers with unsaturated double bonds. The polymerization occurs through chain reactions initiated by radicals, ions, or metal catalysts. Examples include polyethene and polystyrene.
b. Condensation Polymers: Condensation polymers result from the reaction of monomers with two or more functional groups. During polymerization, small molecules like water or alcohol are eliminated as byproducts. Examples include nylon, polyester, and polyurethane.
Based on Molecular Forces:
a. Thermoplastics: Thermoplastic polymers are linear or slightly branched and can be melted and remoulded multiple times without undergoing chemical degradation. The intermolecular forces are weak, allowing for ease of processing and recycling. Examples include polyethene, polypropylene, and polystyrene.
b. Thermosetting Plastics: Thermosetting polymers form crosslinked networks during polymerization and cannot be re-melted or re-moulded once set. They have strong intermolecular forces and show excellent heat resistance and mechanical properties. Examples include phenolic resins and epoxy resins.
Based on Biodegradability:
a. Biodegradable Polymers: These polymers can be broken down into simpler compounds by natural biological processes, reducing environmental impact. Examples include polylactic acid (PLA), polyhydroxyalkanoates (PHA), and certain starch-based polymers.
b. Non-Biodegradable Polymers: Non-biodegradable polymers persist in the environment for extended periods, leading to environmental concerns. Examples include most synthetic polymers like polyethene, polypropylene, and polystyrene.
Understanding the classification of polymers aids in selecting the appropriate material for specific applications, optimising material properties, and promoting sustainability in polymer-based industries. Each class of polymers possesses unique characteristics and is valuable in diverse fields, ranging from packaging materials to advanced engineering applications.