Introduction to Polymers

Introduction to Polymers

• Polymers are long molecules formed by joining thousands of small molecules.
• Macromolecules are another name for polymers.
• Polymerization is the chemical process forming polymers.
• Degree of polymerization is the number of monomer units in a polymer.
• Monomers are small molecules that combine to form polymer molecules.

Nomenclature

• Homopolymer: Polymer containing identical monomer units (e.g., PE, PVC, PVA, PMMA).
• Copolymer: Polymer containing different monomer units (e.g., BUNA-S, BUNA-N, Thiokol).
• Alternate copolymer: Monomers arranged in regular, alternating fashion.
• Block copolymer: Blocks of repeating monomer units followed by blocks of another monomer unit.
• Random copolymer: Monomers randomly distributed along the chain.
• Graft copolymer: Branched structures with different monomer segments on the backbone and branches.
• Functionality: Number of bonding sites in a monomer.

Homochain and Heterochain Polymers

• Homochain polymer: Polymer chains with the same atom type (e.g., PE, PVC).
• Heterochain polymer: Polymer chains with different atom types (e.g., Nylon, Polyester, PU).

Classification of Polymers (Based on various factors)

• Structure/Shape: Linear, Branched, Cross-linked, Atactic, Isotactic, Syndiotactic
• Physical State: Amorphous, Crystalline
• Heat Response: Thermoplastic (soften on heating), Thermosetting (harden on heating, irreversible)
• Conductance: Insulators or Conductors
• Origin: Natural (e.g., cellulose), and Synthetic

Advantages of Polymers over other materials

• Low density leads to the reduction in weight & cost of materials.
• Excellent corrosion resistance.
• Good thermal and electrical insulators.
• Flexible and moldable into desired shapes.
• Low processing temperature.
• Variety of colors & properties.
• Good resistance to chemicals compared to other materials.

Uses of Polymers

• Homes (Windows, flooring, etc.), Vehicles (Windshields, parts), Clothing (Fabrics), Furniture, Appliances, etc.

Polymerisation (Addition/Chain growth & Condensation/Step growth)

• Addition Polymerization chain growth where monomers add to form long chains without elimination of smaller molecules.
• Condensation Polymerization or step growth polymerization.
• Condensation polymerization forms polymers by eliminating small molecules (water, HCl) during the combination of monomers.

Free Radical, Cationic, and Anionic Polymerization

• Free Radical Polymerization: Polymer chains grow through the addition of free radicals.
• Cationic Polymerization: Polymer chains grow through the addition of carbocations.
• Anionic Polymerization: Polymer chains grow through the addition of carbanions.

Plastics

• Plastics are organic materials exhibiting plasticity (moldable).
• Merits: Lightweight, abrasion-resistant, shock-absorbent, inexpensive fabrication, etc.
• Demerits: Low heat resistance, poor ductility, embrittlement at low temperatures, non-biodegradable.
• Classification into Thermoplastic (soften on heating) and thermosetting plastics (rigid and irreversable hardening on heat).

Polyvinyl Chloride (PVC)

• Properties: Hard, stiff, chlorine atom, insoluble, etc.
• Applications: Shoes, pipes, drainage, bottles, car parts, etc.

Phenol Formaldehyde Resin (Bakelite)

• Properties: Hard, rigid, strong, good dielectric properties, heat and moisture resistant, etc.
• Applications: Domestic plugs & switches, handles, adhesives, etc.

Polytetrafluoroethylene (PTFE)

• Properties: Excellent toughness, heat resistant, non-adhesive, etc.
• Applications: Wire insulation, non-stick pans, coating., gaskets, etc.

Fiber Reinforced Plastics (FRP)

• Properties: Excellent strength-to-weight ratio, corrosion resistance, ease of fabrication.
• Preparation: Combination of fibers and resin matrix cured under pressure and/or heat.
• Uses: Aircraft parts, boat hulls, etc.

Elastomers

• Elastomers are polymers with long flexible chains with weak intermolecular forces, they can stretch and return.
• Natural Rubber is a polymer made of isoprene, used in tires, etc.
• Vulcanization involves the treatment of vulcanization with sulfur to improve strength and durability.

Conducting Polymers

• Conducting polymers can conduct electricity.
• Intrinsically conducting polymers: Conjugation in the backbone allows conductance.
• Extrinsically conducting polymers: Conductivity from added conducting elements.
• Applications are in electrochromic displays, solar cells, and sensors.

Biodegradable Polymers

• Biodegradable polymers break down through the action of microorganisms.
• Examples include starch, cellulose, chitin.

Polylactic Acid (PLA)

• Properties: Biocompatibility, processability, high strength.
• Applications: Sutures, stents, food packaging, disposable tableware.

Polyvinyl Acetate (PVA)

• Properties: Transparent, amorphous, chemically resistant.
• Applications: Adhesives, coatings, paints.