- Slides: 19
( Session 41 )
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. http: //www 7. nationalacademies. org/spanishbeyonddiscovery/bio_008231 -01. html
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.
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.
The properties of polymers are very different from the properties of the monomers from which they are formed. F F C=C F F Monomer F F F -C–C–CF F F polymer F F
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.
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
Monomers with double attachments C = C, like tetrafluoroethylene, F 2 C = CF 2, can react with each other by addition reactions. The polymerization of the tetrafluoroethylene produces Teflon: F F F C=C C=C F F F F -C–C–C–CF F Teflon F F
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. CH 2 = CH 2 CH 3 – CH = CH 2 = CH – CH = CH 2
Polymerization by Addition. Ethylene Polyethylene Propylene Polypropylene http: //www 7. nationalacademies. org/spanishbeyonddiscovery/bio_008231 -05. html
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 )
Polyamides are formed by the reaction of condensation within the carboxyl groups and the amine groups of different monomers. [ H 2 N – (CH 2)6 – NH 2 + HOOC – (CH 2)4 – COOH ]n O … - HN – (CH 2)6 – NH - C – (CH 2)4 – C – NH – (CH 2)6 -…+ H 2 O O Polyamide (Nylon)
Polyesters are formed by the reaction of condensation between the carboxylic groups and the alcohol groups of different monomers. [ HO – R 1 – OH + HOOC – R 2 – COOH ]n … - C – O – R 1 – O – C – R 2 – C – O – R 1 – O – C - … O O
Natural rubber Rubber + Sulfur Natural Rubber S S S Stretched Natural Rubber http: //www. inpol. es/images/arbol. jpg
Starch http: //www. cepis. org. pe/eswww/repamar/gtzproye/impacto/image 18. gif
Glycogen http: //www. arrakis. es/~lluengo/gglucogeno. gif
Proteins http: //www. agronort. com/informacion/abcbiotec/FIG 9. gif 00000000 http: //www. inicia. es/de/proteoma/images/peptido. gif
DNA (Deoxyribonucleic Acid)
Monomer Polymer Uses Ethylene Polyethylene Bags, bottles and toys Styrene Polystyrene Molded articles, insulating foam Acrylonitrile Polyacrylonitrile Fibers (orlon, milon) Adipic and Nylon 66 Hexametilen Acid Stockings, cords, fabric, etc. Etylenglycol and Dacron Terephthalic Acid fabric