Definitions [3]
Define thermosetting polymers with two examples of them.
Thermosetting polymers are cross-linked or heavily branched polymers which get hardened during the molding process. These plastics cannot be softened again on heating. Examples of thermosetting plastics include bakelite, urea-formaldehyde resins.
Define rubber.
Polymers which are elastic in nature are called rubber.
Answer the following in one sentence.
Define the term: Vulcanization
The process by which a network of cross-links is introduced into an elastomer is called vulcanization.
Key Points
Key Points: Classification of Polymers> Based on Source or Origin
- Polymers are classified based on their source or origin into three types: natural, semi-synthetic, and synthetic polymers.
- Natural polymers are obtained from plants and animals, such as cellulose, starch, proteins, cotton, and silk.
- Semi-synthetic polymers are chemically modified forms of natural polymers, e.g., cellulose acetate and cellulose nitrate (rayon).
- Synthetic polymers are man-made and prepared in laboratories by polymerisation, such as nylon, polythene, Teflon, and Bakelite.
- Synthetic polymers are further used to make fibres, rubbers, and plastics, which have wide industrial applications.
Key Points: Classification of Polymers> Based on Structure
- Polymers can be classified based on structure into linear, branched, and cross-linked (network) polymers.
- Linear polymers have long, straight chains of monomers joined in a line; e.g., HDPE, PVC, polystyrene.
- Branched polymers have a main chain with side branches of different lengths; e.g., LDPE, polypropylene.
- Cross-linked (network) polymers have chains connected by strong covalent bonds, forming a 3D network structure.
- Cross-linked polymers are hard and rigid due to strong bonding; common examples include Bakelite and melamine.
Key Points: Classification of Polymers> Based on Mode of Polymerisation
- Polymers are classified based on the mode of polymerisation into addition (chain growth), condensation (step growth), and ring-opening polymerisation.
- Addition polymerisation involves repeated addition of monomers (with double/triple bonds) without loss of small molecules; e.g., Teflon, PAN.
- Condensation polymerisation occurs between bi-functional or polyfunctional monomers with elimination of small molecules like water or alcohol; e.g., Nylon, Terylene.
- Ring-opening polymerisation involves polymerisation of cyclic monomers to form long chains, usually without elimination of small molecules; e.g., caprolactam.
Key Points: Classification of Polymers> Based on Intermolecular Forces
- Polymers can be classified based on intermolecular forces into elastomers, fibres, thermoplastics, and thermosetting polymers.
- Elastomers have the weakest intermolecular forces, making them flexible and elastic; e.g., natural rubber, Buna-S.
- Fibres have strong intermolecular forces (like hydrogen bonding), giving them high tensile strength; e.g., Nylon-6, Terylene, PAN.
- Thermoplastics have weak van der Waals forces, so they can be softened and reshaped on heating; e.g., polythene, polystyrene.
- Thermosetting polymers have strong cross-linked structures, making them hard and rigid; e.g., Bakelite, melamine.
Strength order: Elastomers < Thermoplastics < Fibres < Thermosetting polymers.
Key Points: Some Important Polymers
| Polymer | Monomer(s) | Uses |
|---|---|---|
| Natural Rubber (Polyisoprene) | Isoprene (2-methyl-1,3-butadiene) | Exhibits elastic property |
| Neoprene | Chloroprene (2-chloro-1,3-butadiene) | Conveyer belts |
| Buna-S | 1,3-Butadiene + Styrene | Bubblegums, tyres |
| Buna-N | 1,3-Butadiene + Acrylonitrile | Rubber belts, shoe soles, O-rings, gaskets |
| Polypropene | Propene | Ropes, toys, pipes, fibres |
| Polystyrene | Styrene | Insulator, wrapping material, toys, radio & TV cabinets |
| PVC | Vinyl chloride | Rain coats, handbags, vinyl flooring, water pipes |
| Glyptal | Ethylene glycol + Phthalic acid | Paints and lacquers |
| Bakelite | Phenol + Formaldehyde | Combs, phonograph records, electrical switches, wooden planks |
| Nylon 6,6 | Adipic acid + Hexamethylenediamine | Fabrics, ropes, tyre cords |
| Nylon 6 | ε-Caprolactam | Fabrics, ropes |
| Terylene / Dacron | Ethylene glycol + Terephthalic acid | Fibres, safety belts, tents |
| Melamine-formaldehyde | Melamine + Formaldehyde | Unbreakable crockery |
| Urea-formaldehyde resin | Urea + Formaldehyde | Unbreakable cups, laminated sheets |
Key Points: Classification of Polymers> Based on Biodegradability
Polymers are classified as biodegradable or non-biodegradable based on their biodegradability.
1. Biodegradable Polymers
- Meaning: Polymers that decompose by microorganisms or enzymes.
- Nature: Environment-friendly, as they break down naturally.
- Examples: PHBV, Nylon-2–Nylon-6.
- Special point: PHBV is a copolymer used in packaging, medical devices, and drug delivery.
- Use: Helps reduce environmental pollution.
2. Non-Biodegradable Polymers
- Meaning: Polymers that do not decompose by microorganisms.
- Nature: Persist in the environment for a long time.
- Examples: Polythene (LDPE, HDPE), Teflon, Nylon-6,6, PAN.
- Use: Widely used in plastics, fibres, containers, insulation, etc.
- Disadvantage: Causes environmental pollution due to slow decomposition.
Concepts [15]
- Introduction to Polymers
- Classification of Polymers> Based on Source or Origin
- Classification of Polymers> Based on Structure
- Classification of Polymers> Based on Mode of Polymerisation
- Classification of Polymers> Based on Intermolecular Forces
- Classification Based on the Types of Monomeric Units
- Classification Based on the Biodegradability
- Types of Polymerisation Reactions - Copolymerisation
- Types of Polymerisation Reactions - Addition Polymerisation or Chain Growth Polymerisation
- Types of Polymerisation Reactions - Condensation Polymerisation Or Step Growth Polymerisation
- Some Important Polymers
- Types of Polymerisation Reactions - Rubber
- Molecular Mass of Polymers
- Classification of Polymers> Based on Biodegradability
- Polymers of Commercial Importance
