polymer

• Polymer


  Large molecule composed of many repeating sub-units
• Monomer


  The repeating sub-unit of a polymer
• Polymers can have high molecular weight, reaching more than 1,000,000 g/mol
• Types of polymers

  • Homopolymer
  • Copolymer
• Homopolymer


  A polymer containing only one monomer
• Copolymer


  A polymer containing two or more different monomers
• Examples of natural polymers


  • Proteins
  • Carbohydrates
  • Nucleic acids
  • Natural rubber
• Proteins


  • Polymers of amino acids
  • Play a key role in nearly all biological processes
  • Compose 15% of our body
• Carbohydrates


  • Polymers of simple sugars (monosaccharides)
  • Empirical formula is CH2O
  • Functions: food storage/source, structural material
• Nucleic acids


  • Store and transfer genetic information
  • Direct the synthesis of new protein
  • Types: DNA, RNA
• Natural rubber

  • Polymers of isoprene with minor impurities
  • Harvested from rubber trees through 'tapping'
  • Latex is the aqueous suspension of rubber particles
• Types of polymerization

  • Addition polymerization
  • Condensation polymerization
• Addition polymerization


  Linking of monomers into the polymer chain by a chemical reaction that does not produce molecular by-products
• Condensation polymerization


  Small molecules react with each other to form larger structural units while releasing smaller molecules as a byproduct
• Vulcanization


  Chemical process of converting natural rubbers into more durable materials via addition of sulfur

  Forms cross-links between polymer chains, improving the mechanical properties
• Physical properties of polymers

  • Chain length
  • Side group
  • Crystallinity
  • Branching
  • Cross-linking
  • Thermoplastics vs thermosets
• Chain length

  Degree of polymerization<|>Molecular weight<|>Short chains have low melting point and low melt viscosity<|>Long chains have high melting point and high melt viscosity
• Side group

  Polar side groups give stronger attraction between polymer chains, increasing its strength
• Crystallinity


  Higher crystallinity increases the strength and reduces the flexibility of the polymer<|>Highly crystalline polymers have higher strength (e.g. Kevlar)<|>Highly amorphous polymers are more flexible (e.g. rubber)
• Branching


  Branching decreases the crystallinity of polymers, reducing its strength and density
• Cross-linking


  The covalent bond due to cross-linking increases the strength of the polymer
• Thermoplastics


  Soften when heated and become firm when cooled<|>Most popular type of plastics because it can be recycled
• Thermosets


  Soften when heated but harden permanently<|>Cannot be recycled as they decompose when reheated
• Resin identification system


  • PETE
  • HDPE
  • PVC
  • LDPE
  • PP
  • PS
  • Others/Mixed plastics
• PETE (Polyethylene terephthalate)

  Polyester<|>Used for carbonated drinks bottles, fibers, plastic film
• HDPE (High-density polyethylene)


  Used for detergent bottles, milk jugs, and molded plastic cases
• PVC (Polyvinyl chloride)


  Used for wash bottles, shower curtains, clamshell packaging, packaging films, and shrink wrap
• LDPE (Low-density polyethylene)


  Used for drinking straws, yogurt containers, cup for instant noodles, appliances, car fenders, and plastic pressure pipe systems
• PP (Polypropylene)

  Used for packaging foam, food containers, plastic tableware, disposable cups and plates, CD and cassette boxes, some furniture, and computer monitors
• PS (Polystyrene)

  Used for 3-5 gallon water bottles, bullet-proof materials, DVDs, iPod, computer cases, and signs and displays
• Others/Mixed plastics

  Includes acrylic, nylon, polycarbonate, polylactic acid (bioplastic), and multilayer combinations of different plastics
• PTFE/Teflon

  Polytetrafluoroethylene, hydrophobic and has high heat resistance, used as coating of non-stick frying pans and other cookware
• Synthetic rubber


  Also called elastomers, made from petroleum products such as ethylene, propylene, and butadiene, example: polychloroprene (neoprene)
• Nylon

  A synthetic polymer