11.7 Polymers

Definition of Polymers

• Polymerization Reaction: A process where small molecules (monomers) bond to form large molecules called polymers.

• Monomers: The small molecules that react to form polymers.

• Polymer: The large molecule formed by the polymerization of monomers.

• Dimer: A polymer formed by two monomers.

• Trimer: A polymer formed by three monomers.

• Proteins: An example of a polymer in food, formed by amino acids.

Polymers can be classified in different ways, with two main categories based on their structure: Addition Polymers and Condensation Polymers.

11.7.1 Addition Polymers

• Addition Polymerization: A process in which monomer molecules directly connect to form long chains, creating an addition polymer.

Examples of Addition Polymers:

1. Polythene:

• Monomer: Ethene (CH₂=CH₂)

• Process: Ethene reacts at high pressure (1000 atm) and temperature (200°C) with a small amount of oxygen.

• Product: Polythene, a common plastic used for bags and plastic sheets.

2. Polypropene:

• Monomer: Propene (CH₂=CH(CH₃))

• Process: Propene reacts at 140 atm pressure and 120°C temperature in the presence of titanium chloride.

• Properties: Stronger and thicker than polythene; used for ropes, pipes, and carpets.

3. Polyvinyl Chloride (PVC):

• Monomer: Vinyl chloride (CH₂=CHCl)

• Process: Vinyl chloride reacts at high pressure and temperature with organic peroxide.

• Uses: PVC is used for making pipes, wires, and medical devices.

11.7.2 Condensation Polymers

• Condensation Polymerization: A type of polymerization where monomers release small molecules (e.g., H₂O, CO₂) during their formation.

Example:

1. Nylon 6:6:

• Monomers: Adipic acid and hexamethylene diamine.

• Process: These react in the presence of titanium oxide to form Nylon 6:6, releasing water as a by-product.

• Uses: Nylon 6:6 is used for making durable materials like ropes, textiles, and toothbrushes.

11.7.3 Types of Polymers Based on Source

1. Natural Polymers:

• Cellulose and Starch: Found in plants and made of glucose molecules.

• Protein: A polymer of amino acids.

• Natural Rubber: Extracted from rubber trees, commonly used in various products.

2. Synthetic Polymers (Plastics):

• Plastic: Hard, light, cheap, and available in various colors. Plastics can be melted and molded into different shapes.

• Uses: Plastic is used in making pots, containers, pipes, furniture, motor parts, etc.

11.7.4 Advantages and Disadvantages of Using Plastic

Advantages:

• Plastic is widely used to produce daily necessities like containers, bags, pipes, and utensils.

• Compared to metals and natural fibers (e.g., cotton, jute), plastic is thicker, more versatile in shaping, and can be made in various colors.

Disadvantages:

• Environmental Harm: Plastic does not decompose by bacteria or other substances, leading to pollution. It remains in the environment when discarded, harming soil and water.

Our Responsibilities:

• Recycle plastics instead of dumping them.

• Use alternative materials like wood, metal, and natural fibers when possible.

• Biodegradable Plastics: Researchers are working on developing biodegradable plastics, which can reduce environmental damage.

11.7.5 Differences Between Organic and Inorganic Compounds

Organic Compounds Inorganic Compounds

Must have carbon (e.g., Methane, CH₄) Generally do not contain carbon (e.g., Hydrogen Sulfide, H₂S)

Usually take longer to react React more quickly

Formed by covalent bonding Can be formed by ionic or covalent bonding