Polymer Properties and Structure The age of the plastic fantastic

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

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

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

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

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

Addition polymerization has three steps C 2 H 4 is stable – does not spontaneously change into polyethylene – requires severe conditions C 2 H 4 is stable – does not spontaneously change into polyethylene – requires severe conditions 1.Initiation – create reactive species by formation of free radical (unpaired electron) 2.Propagation – As chain grows by addition of C 2 H 4 units, the radical is preserved 3.Termination – radicals eliminated when they meet

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

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

Polymers have revolutionized containers and other household items

Common addition polymers cont’d

Condensation polymers: another route to making chains Two types of monomer required – each capable of making two bonds Two types of monomer required – each capable of making two bonds Bonding occurs between them by elimination of components of water Bonding occurs between them by elimination of components of water OH + H = H 2 O OH + H = H 2 O Lower temperature process than addition polymerization Lower temperature process than addition polymerization

Condensation polymer products

Building Blocks of Proteins Alanine Glycine Leucine Nature’s building blocks contain –CO-NH- C- groups – amide links. The monomers are amino acids. Glycine is the simplest. There are twenty altogether -CO 2 H -NH 2

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)

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

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.

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.

Polymer design is unlimited Applications Applications Nanoelectronics Nanoelectronics Sensors Sensors Catalysis Catalysis Dendrimers