Polymer Properties and Structure

1. Polymer Properties and Structure The age of the plastic fantastic

2. Learning objectives • Describe basic features of a polymer • Name three steps in the addition polymerization process • Distinguish between addition and condensation polymerization • Describe essential features of condensation polymerization • Identify polymerization process used on basis of polymer composition

3. Polymers are large molecules made by concatenation of many small units • Building blocks are monomers • A polymer may contain thousands of monomers and have a molar mass of hundreds of thousands • Homopolymer – the monomers are identical • Copolymer – the monomers are different (2 or more)

4. Monomer • A monomer must be capable of forming two bonds to generate a chain • A double bond meets that requirement

5. Two main synthetic approaches • Addition polymerization • Simply adding monomers together – synthetic plastics • Condensation polymerization • Combination by exclusion of a small molecule (usually water) – extensively used by nature

6. Reactive radical to initiate the process • Radicals are reactive – contain unpaired electrons • Odd + even = odd: unpaired electron survives ● R R R●

7. Addition polymerization has three steps • C2H4 is stable – does not spontaneously change into polyethylene – requires severe conditions • Initiation – create reactive species by formation of free radical (unpaired electron) • Propagation – As chain grows by addition of C2H4 units, the radical is preserved • Termination – radicals eliminated when they meet

8. Polymer properties tuned by modifying added groups • Density • Polarity • Chain branching • Cross linking • Chain length

9. Structure is function • HDPE: the strands pack closely together • LDPE: branches prevent close packing

10. Polymers have revolutionized containers and other household items

11. Common addition polymers cont’d

12. Condensation polymers: another route to making chains • Two types of monomer required – each capable of making two bonds • Bonding occurs between them by elimination of components of water • OH + H = H2O • Lower temperature process than addition polymerization

13. Condensation polymer products

14. Building Blocks of Proteins Nature’s building blocks contain –CO-NH-C- groups – amide links. The monomers are amino acids. Glycine is the simplest. There are twenty altogether Glycine Alanine Leucine -NH2 -CO2H

15. Polypeptide Chains Condensation of amino acids creates polypeptide chains. Hemoglobin contains four chains, which imprison an iron atom. The iron atom binds with oxygen (or CO or cyanide ion)

16. The amide link • Why –CO-NH-C- (amide) rather than –CO-O-C- (ester)? • No facility for H-bonding in –CO-O-C- • H atom in –CO-NH-C- provides H-bonding for secondary structure control

17. Hair and Wool Secondary and tertiary structures of peptide chains (α-keratin) in the structure of hair. Hydrogen bonding plays a crucial role in this process.

18. Glucose and Cellulose Cellulose is a condensation polymer of the simplest carbohydrate, glucose. Only C,H and O are involved. Cellulose is the most abundant organic chemical on earth.

19. Polymer design is unlimited • Applications • Nanoelectronics • Sensors • Catalysis Dendrimers