PolymersChapter 1

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• 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 ?

POLYMER STRUCTURES

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Polymer

Poly mer many repeat unit (building blocks)

C C C C C C

HHHHHH

HHHHHH

Polyethylene (PE)

ClCl Cl

C C C C C C

HHH

HHHHHH

Poly(vinyl chloride) (PVC)

HH

HHH H

Polypropylene (PP)

C C C C C C

CH3

HH

CH3CH3H

repeatunit

repeatunit

repeatunit

Carbon chain backbone

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Chemistry and Structure of Polyethylene

•Polyethylene is a long-chain hydrocarbon. •Top figure shows repeat unit and chain structures. •Other figure shows zigzag backbone structure.

Tetrahedral arrangement of C-H

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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

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

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The International Journal for the Science and Technology of Polymers

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

• 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 90-120 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

Biodegradable Polymers as Drug Carrier Systems

Commercial Suture materials

Braided Polyester Multifilament nylon

Polythetrafluoroethylene

Polymers in Everyday Life

• 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)• Just about everywhere!

Compact Discs

• 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.

Plastic

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…..

Rigid Strong Easy to fabricate Dimensional stability

Thank you!