Transcript Document

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 today’s experiment you will make
nylon, slime, and silicone rubber.
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
CLASSIFYING POLYMERS BY SYNTHESIS
• Addition polymers are made from monomers that link together without
losing any atoms. These monomers typically have at least 1 carboncarbon 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.
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.
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.
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.
• The Food and Drug Administration (FDA)
has warned that the plasticizer di(2ethylhexyl)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.
• Similarly, the National Institutes of Health (NIH) reports that PVC
flooring in bedrooms is associated with asthma and allergies in
children.
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.
• 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.
• Thermoset plastics cannot be recycled by resoftening and
remolding. Therefore, they should not be used for
“disposable goods”.
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.
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.
SAFETY
• Give at least 1 safety concern for the following procedures
that will be used in today’s experiment.
• Using 20 % NaOH, 5 % aqueous hexamethylene diamine, 5
% sebacoly chloride in cyclohexane, 4 % polyvinyl alcohol,
4 % borax solution, sodium silicate (water glass), and 1propanol.
• 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.
SOURCES
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Parental Concerns. http://www.healthofchildren.com/I-K/Intravenous-Rehydration.html
Available: [accessed 3 February 2007].
• BBC. 2002. BBC NEWS | UK | Fire Strike Tests Armed Forces.
http://news.bbc.co.uk/1/hi/uk/2501695.stm Available: [accessed 3 February 2007].
• Environmental Health Perspectives. 2004. Children’s 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/dehp.html Available:
[accessed 3 February 2007].
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Inc.
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Available: [accessed 3 February 2007].
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[accessed 3 February 2007].