1. Polymers
( Session 41 )

2. Polymers
Organics
A key discovery at the end of XIX century was that carbon atoms can form bonds with up to four more atoms, organized in such a form that they form the corners of a tetrahedron or pyramid. Many carbon atoms can bond forming molecular chains of great length or polymers, in thousands of millions of different combinations.

3. Polymers
Polymers are very large molecules that have hundreds or thousands of atoms. They are characterized for having a high molecular weight that oscillates between the thousands and millions of grams.
They are also known as macromolecules.
Polymers are formed by the union of many chemical units known by the name of monomers.
Monomers are chemical compounds that react with themselves ir with other different monomers to form macromolecules or polymers. Polymers formed by two or more different monomers are known as copolymers.

4. Natural or Synthetic
Natural polymers are the root of all the processes of life, and our technological society depends greatly on synthetic polymers.
Examples of natural polymers: proteins, polysaccharides like starch and cellulose, nucleic acids natural rubber, glue, etc.
Examples of synthetic polymers: nylon, dacron, teflon, polyethylene , polypropylene, PVC, polystyrene, polyacrylonitrile , etc.

5. Properties
The properties of polymers are very different from the properties of the monomers from which they are formed.
F F F F F F F
C = C C – C – C – C – C -
F F F F F F F
Monomer polymer

6. The great variety of polymers that exist makes it impossible to define common characteristics for them, because depending on their production process and the materials used polymers can very diverse characteristics: resistance to crashes, resistant to heat, flexible, soft, hard, elastic, impermeable, resist to oxidization, to acids, biodegradable or not, low and high density, etc.

7. Synthetic polymers are fabricated taking advantage of the chemical conduct of the functional group of their monomers.
From this there are two known types of polymerization reactions:
Polymerization by addition
Polymerization by condensation

8. Polymerization by Addition
Monomers with double attachments C = C, like tetrafluoroethylene, F2C = CF2, can react with each other by addition reactions. The polymerization of the tetrafluoroethylene produces Teflon:
F F F F F F F F F F F F
C = C C = C C = C  C – C – C – C – C – C -
F F F F F F F F F F F F
Teflon

9. In a polymerization by addition reaction, the pi bonds are broken and the electrons form new sigma bonds between the units of the monomer. Many alkenes are used to synthesize the polymers.
CH2 = CH2
CH3 – CH = CH2
CH2 = CH – CH = CH2

10. Examples Ethylene Polyethylene Propylene Polypropylene
Polymerization by Addition.
                                             
Ethylene Polyethylene
Propylene Polypropylene

11. Polymerization by Condensation
The most important polymers that are obtained from this type of reaction are polyamides and polyesters.
Important polyamides : Nylon and Kevlar
Important polyesters : Dacron and PET (Polyethylenterephtalat )

12. Polymerization by Condensation
Polyamides are formed by the reaction of condensation within the carboxyl groups and the amine groups of different monomers.
[ H2N – (CH2)6 – NH2 + HOOC – (CH2)4 – COOH ]n O
… - HN – (CH2)6 – NH - C – (CH2)4 – C – NH – (CH2)6 -…+ H2O
O Polyamide (Nylon)

13. Polymerization by Condensation
Polyesters are formed by the reaction of condensation between the carboxylic groups and the alcohol groups of different monomers.
[ HO – R1 – OH + HOOC – R2 – COOH ]n
… - C – O – R1 – O – C – R2 – C – O – R1 – O – C - …
O O O O

14. Natural Polymer Natural rubber Rubber + Sulfur  Natural Rubber S S S
Stretched Natural Rubber

15. Natural Polymers Starch

16. Natural Polymers Glycogen

17. Natural Polymers Proteins

18. Natural Polymers
DNA (Deoxyribonucleic Acid)

19. Some Natural Polymers Monomer Polymer Uses Ethylene Polyethylene
Bags, bottles and toys
Styrene
Polystyrene
Molded articles, insulating foam
Acrylonitrile
Polyacrylonitrile
Fibers (orlon, milon)
Adipic and Hexametilen Acid
Nylon 66
Stockings, cords, fabric, etc.
Etylenglycol and Terephthalic Acid
Dacron
fabric