An Introduction to Polymers “Plasticus, that which can be molded” Addition Polymerisation Condensation Polymerisation

Polymers Are long chain molecules that are formed by the joining together of a large number of repeating units called monomers by a process of polymerization. (DNA, protein, plastics, rubber, cotton)

Uses of Polymers Cotton

Uses of Polymers Rubber

The decks, fence, stepping stones, house shingles, and the sweat shirt, were all made from recycled plastic.

Uses of Polymers World’s largest rubber band ball – 8200 lb

Uses of Polymers Bulletproof glass

Uses of Polymers Plastics

Uses of Plastics

Uses of Plastics Garbage Islands

Polymers To categorize polymers we can sort them out as synthetic (plastics) or natural. Synthetic polymers can be differentiated based on their response to heat. Thermoplastic polymers soften and melt when heated. Thermoset polymers do not soften or melt when heated.

Thermoplastic polymers Long chain hydrocarbons have mainly van der Waals forces with some dipole forces due to substituted groups. (so can slide due to weak attraction) Can be remolded. (parafilm demo)

Thermoset polymers The chains are cross-linked by covalent bonds We can control the amount of cross-linking and hence the strength of the plastic.

Thermoset polymers

Thermoplastic vs Thermoset n a P o l y m T s b d , w u f p . W g S t r e c h C o s - L i n k d P l y m T a g . W , p w u ' f R x

Polymer Production Addition Polymers – monomers are linked through addition reactions Condensation Polymers – monomer units are linked through condensation reactions (a small molecule is formed as a by product)

Addition Polymerization Ethene H2C CH2 ethene CH2 Polyethylene – insulating wires, plastic containers 6

Addition Polymerization Propene propene H2C CHCH3 CH CH3 Polypropylene – rope, carpets 6

Addition polymerization Examples Polycholorethene – PVC, raincoats Methyl methacrylate – plexiglass Tetrafluroethene - Teflon CHCl CH2 CF2 CF2

Addition Polymerisation The polymer is the only product Involves the opening out of a double bond Reaction proceeds by a free radical mechanism A small amount of oxygen is needed to begin reaction.

Mechanism Initiation .. RO • H2C CHCH3 7

Mechanism Initiation .. RO • H2C CHCH3 7

.. RO: Mechanism H2C CHCH3 • 9

Mechanism Propagation .. RO: H2C CHCH3 • CHCH3 H2C 10

.. RO: Mechanism H2C CHCH3 H2C CHCH3 • 10

.. RO: Mechanism H2C CHCH3 H2C CHCH3 CHCH3 H2C • 10

.. RO: Mechanism H2C CHCH3 H2C CHCH3 H2C CHCH3 • 10

.. RO: Mechanism H2C CHCH3 H2C CHCH3 H2C CHCH3 CHCH3 H2C • 10

Mechanism Termination .. RO: H2C CHCH3 H2C CHCH3 H2C CHCH3 CHCH3 H2C • • RO: 10

Mechanism Termination .. RO: H2C CHCH3 H2C CHCH3 H2C CHCH3 CHCH3 H2C RO: 10

Ethylene has two carbons which have a doublebond between them Ethylene has two carbons which have a doublebond between them. High temperature or UV light can cause two of these shared (paired) electrons to become unshared (unpaired). C H H H These unpaired electrons are eager to pair up with another electron. If this ethylene molecule bumps another ethylene molecule, the unpaired electrons will cause the one it bumped into to lend one of its inner electrons. C C - - C C H H - - C - C - - - C C - -

Here’s another way to see the chain reaction Here’s another way to see the chain reaction. These are the carbon atoms with their double-bond (2 shared electrons each). The hydrogen atoms are not shown. A collision breaks the first bond. Once the first double bond is broken, a chain reaction will occur. In about a second an entire chamber of compressed ethylene gas turns into the polymer, polyethylene.

Properties of Plastics Plastics used as containers for a number of substances so need to be unreactive. Converting (alkenes) into single bond (alkane) molecules become fairly stable and unreactive.

Cross - Linking Monomers with two double bonds can be used (increases strength. Why?) i.e. Neoprene Monomer Similar to natural rubber Because of 2 double bonds able to add chains in multiple directions Cl CH2 C CH CH2

Cross - Linking CH2 C CCl New bonds Cross Links CH2 CCl CH2 C

Cross - Linking We can control the rigidity depending on the number of dienes in the starting monomers. i.e. polyethylene with varying amounts of dienes is used to make garbage bags, fencing and netting to wrap trees.

Condensation Polymerization Polyester Polyester is made from the two monomers, terephthalic acid (note: “ph” is silent) and ethylene glycol (car antifreeze). This makes a popular plastic called PETE, which is short for Polyethylene Terephthalate. The synthesis is also a dehydration reaction because water is given off.

Condensation Polymerization Polyester OH PETE HO O OH + O o C c o o o H O dioic acid diol dioic acid diol dimer/copolymer

Condensation Polymerization Polyester O O O O HO R O R R O R O R R OH H2O H2O H2O Hence the name Polyester ESTER groups formed

Condensation Polymerization Nylon (polyamide) Tetramethylene dicarboxylic acid (adipic acid) Hexamethylene diamine methylene x 6 (hexa) amine x 2 (di) Nylon is actually a “copolymer” or dimer because is it made from two monomers. Nylon was discovered in 1935. The name nylon is derived from two cities where it was discovered namely New York (NY) and London (LON). dehydration reaction is a condensation reaction with water as the molecule that comes off.

Condensation Polymerization Nylon (polyamide)

Condensation Polymerization Nylon (polyamide) Dehydration Reaction

Condensation Polymerization Kevlar (polyamide)

Condensation Polymerization Kevlar (polyamide) Used in bullet proof vests stronger than steel

Uses of polyamides The main use of polyesters and polyamides is as fibres in clothing. Most clothing now has a degree of manufactured fibres woven into the natural material (such as cotton). This gives the material more desirable characteristics, such as stretchiness, and better washability. Also are used in baby diapers, polymethylacrylate – crystal polymer used to absorb water

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