POLYMERS

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POLYMERS
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Polymer

• A very large molecule formed by the covalent
  bonding of repeating smaller molecules
  (monomers).
• Monomers can be identical or different
• Example of a notation of a polymer
• (-CH2-CH2-)n indicates the unit inside the ( )
  is repeated n times, where n is a very large
  number.
• May be natural or synthetic

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Natural polymers

• Examples
• polysaccharides (starch, cellulose)
• long chains of monosaccharides

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• DNA, RNA
• long chains of nucleotides
• proteins
• long chains of amino acids

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Synthetic Polymers

• Examples
• Nylon
• Polyester
• Plastics
• Polyethylene (trash bags, plastic containers)
• Polyvinyl chloride (plastic wrap)
• Polystyrene (styrofoam)
• Teflon

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What Makes Polymers Unique?

• Really big molecules (macromolecules) like
  polymers have very different properties than
  small molecules

• Chain entanglement Long polymer chains get
  entangled with each other.
• When the polymer is melted, the chains can flow
  past each other.
• Below the melting point, the chains can move, but
  only slowly. Thus the plastic is flexible, but
  cannot be easily stretched.
• Below the glass transition point, the chains
  become locked and the polymer is rigid

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Physical Properties
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General Types of Polymer Formation

• Addition Polymers
• No loss of any atoms from the monomers when
  linked
• Ex) PVC, styrofoam, polyethylene

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• Condensation Polymers
• loss of atoms (usually -H and OH forming a water
  molecule) when monomers are linked
• Ex) polyester, nylon, polysaccharides, proteins

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Polyethylene

• Produced in greater quantity than any other
  synthetic polymer
• Stable, resistant to chemical attack, cheap to
  produce
• Varying the type of catalyst and changing the
  temperature and pressure allows polyethylene with
  different properties to form

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• Low Density Polyethylene (LDPE)
• At higher temps and pressure, short chain
  polymers with irregular branching form in which
  the chains are not closely packed
• This is very flexible, used in food wrap, trash
  bags, squeeze bottles, etc.

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• High Density Polyethylene (HDPE)
• At lower temps, pressure, and a different
  catalyst, the chains formed are closely packed
• 1/3 of all polyethylene produced in the US is
  HDPE
• It is strong, tough, rigid