CH 104: THE SYNTHESIS OF COMMON POLYMERS

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CH 104 THE SYNTHESIS OF COMMON POLYMERS

• Polymers are long chains of repeating units
  called monomers. Literally, polymers are many
  (poly) small units (meros). Monomers are one
  (mono) small unit (mero).
• Examples of natural polymers include DNA and RNA
  (from nucleic acids), proteins (from amino
  acids), starch and cellulose (from glucose), and
  rubber (from isoprene).

• Examples of manmade polymers include
  polyethylene, polypropylene, polyester,
  polyurethane, polyvinylchloride (PVC), epoxy,
  nylon, slime, silicone rubber, Dacron, Kevlar,
  Lucite, Orlon, and Teflon.
• In todays experiment you will make nylon, slime,
  and silicone rubber.

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CHEMICAL STRUCTURES OF POLYMERS

• In simplest terms, a polymer is made by
  repeatedly adding 1,000 to 1,000,000 or more
  monomers to a molecule.
• Many A ? etc. A A A A etc. or ( A
  )n
• A copolymer has 2 or more alternating monomers.
• Many A Many B ? etc. A B A B etc. or
  ( A B )n

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CLASSIFYING POLYMERS BY SYNTHESIS

• Addition polymers are made from monomers that
  link together without losing any atoms. These
  monomers typically have at least 1 carbon-carbon
  double bond. Polyethylene is an addition
  polymer.
• Condensation polymers are made from monomers that
  link together and lose small molecules such as
  water (H2O), ammonia (NH3), or hydrogen chloride
  (HCl). These monomers have 2 or more reactive
  functional groups. Most condensation polymers
  are copolymers. Dacron is a condensation polymer.

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CLASSIFYING POLYMERS BY STRUCTURE

• Polyethylene is a linear polymer.
• Polypropylene is a branched polymer.
• Kevlar is a cross-linked polymer.
• The polymer chains of Kevlar crystallize in
  parallel, like dry spaghetti noodles in a box.
  These parallel chains are cross-linked with
  hydrogen bonds. As a result, Kevlar is 5 times
  stronger than steel. It is used in bulletproof
  vests, helmets, suspension bridge cables, and
  radial tires.

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CLASSIFYING POLYMERS BY THERMAL PROPERTIES

• Linear and branched polymers are long molecules
  that are more or less crystalline. They interact
  in these crystals through weak dipole-dipole
  forces. These weak dipole-dipole forces allow
  the crystals to soften when heated. These
  softened polymers can be molded or extruded into
  other shapes. Therefore, linear and branched
  polymers are often called thermoplastics.
  Polyethylene (an addition polymer) and nylon (a
  condensation polymer) are thermoplastics.

• In contrast, a cross-linked polymer is
  essentially 1 gigantic molecule. The cross-links
  are strong bonds that make an irregular
  3-dementional structure. Therefore, these
  thermoset plastics do not soften when heated. In
  fact, heating can produce more cross-links and
  make the material even harder. Kevlar is a
  thermoset plastic.

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PROBLEMS WITH PLASTICS

• PLASTICIZERS AND HEALTH Plasticizers are often
  added to synthetic polymers to make the final
  product soft and pliable. If plasticizers are
  not added, these products would be hard, brittle,
  and useless for many purposes.
• Similarly, the National Institutes of Health
  (NIH) reports that PVC flooring in bedrooms is
  associated with asthma and allergies in children.

• The Food and Drug Administration (FDA) has warned
  that the plasticizer di(2-ethylhexyl)phthalate
  (DEHP) produces a range of adverse effects in
  laboratory animals and might cause adverse
  events in humans. The FDA has further warned
  that DEHP is released from polyvinyl chloride
  (PVC) medical devices, including intravenous (IV)
  bags, blood storage bags, feeding bags, dialysis
  bags, catheters, and various tubing.

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PROBLEMS WITH PLASTICS

• DISPOSAL Plastics do not corrode, do not rust,
  and last almost indefinitely. Unfortunately,
  these desirable properties are a problem when
  plastics are thrown away. They do not
  biodegrade.
• Thermoset plastics cannot be recycled by
  resoftening and remolding. Therefore, they should
  not be used for disposable goods.

• Fortunately, most plastic wastes are recyclable.
  Plastic wastes are about 85 polyethylene,
  polypropylene, polystyrene, and
  polyvinylchloride. These are all thermoplastics
  and can be resoftened and remolded into new goods.

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PROBLEMS WITH PLASTICS

• FIRE HAZARDS Toxic gases are sometimes released
  when plastics burn. For example, hydrogen
  cyanide (HCN) is released when polyacrylonitriles
  burn. And hydrogen chloride (HCl) is released
  when polyvinylchloride (PVC) burns.

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PROBLEMS WITH PLASTICS

• DEPENDENCE ON FOSSIL FUELS Plastics use fossil
  fuels as a raw material and as a source of energy
  for manufacturing. Unfortunately, fossil fuels
  are nonrenewable and will one day be gone.

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SAFETY

• Give at least 1 safety concern for the following
  procedures that will be used in todays
  experiment.
• Using 20 NaOH, 5 aqueous hexamethylene
  diamine, 5 sebacoly chloride in cyclohexane, 4
  polyvinyl alcohol, 4 borax solution, sodium
  silicate (water glass), and 1-propanol.
• These are irritants. Wear your goggles at all
  times. Immediately clean all spills. If you do
  get either of these in your eye, immediately
  flush with water.
• In addition, many of these reagents are
  flammable.
• Finally, you must wear protective gloves at all
  times.
• Your laboratory manual has an extensive list of
  safety procedures. Read and understand this
  section.
• Ask your instructor if you ever have any
  questions about safety.

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SOURCES

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• BBC. 2002. BBC NEWS UK Fire Strike Tests
  Armed Forces. http//news.bbc.co.uk/1/hi/uk/250169
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• Environmental Health Perspectives. 2004.
  Childrens Exposure to Common Plasticizers Linked
  to Increased Risk of Asthma, Allergies.
  http//www.ehponline.org/092404a.html Available
  accessed 3 February 2007.
• Food and Drug Administration. 2002. FDA Public
  Health Notification PVC Devices Containing the
  Plasticizer DEHP. http//www.fda.gov/cdrh/safety/d
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