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Polymers
Chapter 1
1
POLYMER STRUCTURES
• What are the general structural and chemical
characteristics of polymer molecules?
• What are some of the common polymeric
materials, and how do they differ chemically?
• How is the crystalline state in polymers
different from that in metals and ceramics ?
2
Polymer
Poly
many
mer
repeat unit (building blocks)
repeat
unit
repeat
unit
H H H H H H
C C C C C C
H H H H H H
H H H H H H
C C C C C C
H Cl H Cl H Cl
Polyethylene (PE)
Poly(vinyl chloride) (PVC)
repeat
unit
H
C
H
H H
C C
CH3 H
H H
C C
CH3 H
H
C
CH3
Polypropylene (PP)
Carbon chain backbone
3
Chemistry and Structure of Polyethylene
Tetrahedral
arrangement
of C-H
•Polyethylene is a long-chain hydrocarbon.
•Top figure shows repeat unit and chain structures.
•Other figure shows zigzag backbone structure.
4
Ancient Polymers
• Naturally occurring polymers (those derived
from plants and animals) have been used for
centuries.
– Wood
– Rubber
– Cotton
– Wool
– Leather
– Silk
• Oldest known uses
– Rubber balls used by Incas
5
Cellulose
• Cellulose is a highly abundant organic compound.
Extensive hydrogen bonding between the chains causes
native celluose to be roughly 70% crystalline. It also
raises the melting point (>280°C) to above its
combustion temperature.
• Cellulose serves as the principal structural component
of green plants and wood.
• Cotton is one of the purest forms of cellulose and has
been cultivated since ancient times.
• Cotton also serves (along with treated wood pulp) as the
source the industrial production of cellulose-derived
materials which were the first "plastic" materials of
commercial importance.
Rubber
• A variety of plants produce a sap consisting of a colloidal
dispersion of cis-polyisoprene. This milky fluid is especially
abundant in the rubber tree (Hevea); it drips when the bark is
wounded.
• After collection, the latex is coagulated to obtain the solid
rubber. Natural rubber is thermoplastic, with a glass transition
temperature of –70°C.
• Raw natural rubber tends to be sticky when warm and brittle
when cold, so it was little more than a novelty material when first
introduced in Europe around 1770.
• It did not become generally useful until the mid-nineteenth
century when Charles Goodyear found that heating it with sulfur
— a process he called vulcanization — could greatly improve its
properties.
cis-polyisoprene
The International Journal for
the Science and Technology of
Polymers
8
Polymer for Medical Applications
Biodegradable Polymers as
Drug Carrier Systems
• Polyesters
– Lactide/Glycolide Copolymers
• Have been used for the delivery of steriods,
anticancer agent, antibiotics, etc.
• PLLA is found as an excellent biomaterials and
safe for in vivo (Lactic acid contains an
asymmetric α-carbon atom with three different
isomers as D-, L- and DL-lactic acid)
• PLGA is most widely investigated
biodegradable polymers for drug delivery.
• Lactide/glycolide copolymers have been
subjected to extensive animal and human trials
without any significant harmful side effects
Biodegradable Polymers as
Drug Carrier Systems
• Poly(amides)
– Natural Polymers
• Remain attractive because they are natural
products of living organism, readily
available, relatively inexpensive, etc.
• Mostly focused on the use of proteins such
as gelatin, collagen, and albumin
Biodegradable Polymers as
Drug Carrier Systems
• Polymer Processing
– Drug-incorporated matrices can be
formulated either compression or
injection molding
– Polymer & drug can be ground in a
Micro Mill, sieve into particle size of 90120 µm, then press into circular disc
– Alternatively drug can be mixed into
molten polymer to form small chips,
then it is fed into injection molder to
mold into desired shape
Commercial Suture materials
Braided Polyester
Multifilament nylon
Polythetrafluoroethylene
Polymers in Everyday Life
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Clothing
Oil recovery
Food and flavors
Agriculture
Packaging
Consumer items – clothing, toys, skin care
Automotive parts
Industrial (pipes, parts, additives, etc)
Electronics
Medicines (proteins, antibodies, coatings
for tablets, gel caps)
Compact Discs
Plastic
• A compact disc (or CD) is an optical disc used for storing
digital data. It was originally invented for digital audio in
1979.
• Compact discs are made from a 1.2 mm thick disc of plastic
coated with a much thinner aluminum layer.
• Aluminum layer is protected by a film of lacquer, which can
be printed with a label.
• Injection molding is used to manufacture compact discs.
Candidate 1- Polyethylene
•
Produced from petroleum product (ethylene), most commonly used
polymer in consumer applications.
•
Provide toughness, rigidity and strength for blow molding
applications, extruded products, films, and injection molded items.
•
Excellent combination of stiffness and resistance to
chemicals/liquids.
•
Key applications
– Containers- shampoo, detergent, milk, solvents and oils
– Bays, garbage can liners
– Toys, tote bins
Candidate 2- Polystyrene
•
First produced in 1938 by The Dow Chemical Company.
•
Made from monomer styrene, another petroleum based product.
•
Protects products against moisture, maintains strength and shape
over long periods of time (sturdy).
•
Key applications
– Foam- egg cartons, insulation, packing materials,
– Food trays, cups
– Boxes for small objects, plastic utensils, cups
– Large and portable appliances
Candidate 3- Polycarbonate
• Polymers with carbonate functional groups in the
backbone.
• Very durable, transparent material, high heat and scratch
resistance, resistance to chemicals/liquids.
• Key applications
– Bullet proof glass, safety wear (shields, glasses)
– Automotive headlamp lenses
– Bottles, high end tableware, computer housing
– Medical equipment
More About Polycarbonate
The material of choice is…..
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Rigid
Strong
Easy to fabricate
Dimensional stability
Thank you!