Polymers & its Examples | Chemistry for JAMB PDF Download

Polymers: Natural and Synthetic Rubber

1. Natural Rubber

• Natural rubber is a polymer derived from the latex of certain plants, primarily the rubber tree (Hevea brasiliensis).
• It is composed of repeating units of the monomer isoprene.
• Methods of preparation:
• Extraction: Natural rubber is obtained by tapping the rubber tree to collect the milky latex sap, which is then coagulated to form rubber sheets.
• Coagulation: The collected latex is treated with acid or other coagulating agents to solidify the rubber.
• Uses: Natural rubber is widely used in the manufacture of tires, rubber bands, gloves, footwear, adhesives, and various other products due to its excellent elasticity and flexibility.

2. Synthetic Rubber

• Synthetic rubber is a man-made polymer designed to mimic the properties of natural rubber.
• It is produced through the polymerization of various monomers.
• Methods of preparation:
  • Polymerization: Synthetic rubber is prepared by polymerizing monomers such as butadiene, styrene, or isoprene.
  • Copolymerization: Two or more monomers can be copolymerized to produce synthetic rubbers with specific properties.
• Examples:
  • Styrene-butadiene rubber (SBR): It is a copolymer of styrene and butadiene and is commonly used in tire manufacturing.
  • Neoprene: It is a polymer of chloroprene and is known for its excellent resistance to heat, oil, and chemicals.
• Uses: Synthetic rubber finds applications in the production of automobile tires, conveyor belts, gaskets, seals, hoses, and many other industrial products.

Thermoplastic and Thermosetting Plastics

1. Thermoplastic Plastics

• Thermoplastic plastics are a type of polymer that can be repeatedly melted and solidified without undergoing significant chemical changes.
• They have linear or branched molecular structures.
• Methods of preparation:
  • Polymerization: Thermoplastic plastics are prepared by polymerizing suitable monomers using methods like addition polymerization or condensation polymerization.
  • Molding: The resulting polymer can be molded into desired shapes through techniques such as injection molding, blow molding, or extrusion.
• Examples:
  • Polyethylene (PE): It is a widely used thermoplastic polymer known for its high strength, flexibility, and resistance to chemicals. It is used in packaging, pipes, and various household products.
  • Polyvinyl chloride (PVC): PVC is a versatile thermoplastic that is used in construction materials, electrical insulation, pipes, and vinyl records.
• Properties: Thermoplastic plastics can be easily recycled, reshaped, and reused due to their reversible nature.

2. Thermosetting Plastics

• Thermosetting plastics are polymers that undergo irreversible chemical changes upon curing and cannot be melted or reshaped after they have solidified.
• They have highly cross-linked three-dimensional structures.
• Methods of preparation:
  • Polymerization and cross-linking: Thermosetting plastics are prepared by polymerizing monomers with cross-linking agents or through a curing process involving heat, pressure, or chemicals.
  • Molding: The uncured polymer mixture is molded into the desired shape, and then curing takes place to harden the material.
• Examples:
  • Phenolic resins: They are used in electrical components, coatings, adhesives, and molded objects due to their excellent heat resistance and electrical insulation properties.
  • Epoxy resins: Epoxy resins are widely used in composites, adhesives, coatings, and electrical applications due to their high strength, chemical resistance, and adhesive properties.
• Properties: Thermosetting plastics are rigid, durable, and have high heat and chemical resistance, making them suitable for applications requiring dimensional stability and strength.