Polymerisation PDF

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lecture notes on polymerisation...

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Polymerisation Addition polymers    

Polymers are large molecules that are built up from small molecules called monomers They occur naturally in proteins, DNA etc Addition polymers are made from monomers with a C=C bond. When the monomers polymerise, the double bond opens and the monomers bond together to form a backbone of carbon atoms.

R -H -CH3 -Cl -C ≡ N

Name of polymer Poly(ethene) Poly(propene) Poly(chloroethene) Poly(propanenitrile) Poly(phenylethene)

Trade name Polythene / Alkathene Polypropylene PVC (polyvinyl chloride) Acrylic / Courtelle Polystyrene

Uses Films, plastic bags Moulded plastics, fibres Pipes, flooring Fibres Packaging, insulation

Biodegradability   

Poly alkenes are long chain saturated alkane molecules They have strong non polar C-C and C-H bonds so they are very unreactive molecules They are not attacked by biological agents such as enzymes and so they are not biodegradable.

Condensation Polymers   

A condensation reaction occurs when two molecules react together and a small molecule often water or hydrogen chloride is eliminated. Condensation polymers are normally made from two different monomers, each of which has two functional groups and both functional groups can react so that a long chain polymer results. Polyesters, polyamides and polypeptides are all examples of condensation polymers.

Polyesters  

Polyesters have an ester linkage –COO- repeated over and over again To make a poly ester we use diols, which have two –OH groups, and dicarboxylic acids which have two carboxylic acid –COOH groups.

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The functional groups on the ends of each molecule react to form a chain. The diols and dicarboxylic acids react together to give a poly ester by eliminating molecules of water.

Example 1

The fibre Terylene is a polyester. It is made from

This is the repeating unit

Polyamides

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Polyamides have the amide linkage –CONH- repeated To make polyamides from two different monomers, a diaminoalkane (which has two amino groups) reacts with a dicarboxylic acid (which has two carboxylic acid groups) Both Nylon and Kevlar are condensation polymers. Polypeptides are also polyamides. In a polypeptide, each amino acid has both an amine group and a carboxylic acid group. So the amine group of amino acid can react with the carboxylic acid group of another. A molecule of water is eliminated and a condensation polymer can begin to form.

Nylon-6,6  

Nylon 6,6 is made from 1-6, diamino hexane and hexane-1,6-di carboxylic acid industrially. and

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In the lab, the reaction goes faster if a diacid chloride is used rather than the dicarboxylic acid and in this case hydrogen chloride is eliminated instead of water. The 1,6-diaminohexane is used just as before, but hexanedioyl dichloride is used instead of hexanedioic acid.

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Kevlar 

Kevlar is made from benzene-1,4-diamine and benzene-1,4-dicarboxylic acid

 Indentifying the monomers of a condensation polymer   

Start with the repeating unit Break the linkage at C-O from a polyester or C-N for a polyamide Add back the components of water for each ester or amide link

Disposal of polymers    

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Poly alkenes can be burnt to carbon dioxide and water to produce energy although poisonous carbon monoxide may be released into the atmosphere if combustion is incomplete. Burning poly alkenes adds to the problem of increasing the level of CO2 in the atmosphere. Other addition polymers like polystyrene may release toxic products on burning. Complete combustion of polystyrene would produce carbon dioxide and water only. However under certain conditions the polymer may depolymerise to produce toxic styrene vapour. Incomplete combustion produces black smoke containing carbon monoxide and un burnt carbon. Condensation polymers like polyesters and polyamides can be broken down by hydrolysis and are potentially biodegradable by the reverse of the polymerisation reaction by which they were formed. The reaction is very slow.

Recycling plastics    

Poly ester materials are now being collected, sorted and then melted and reformed. Almost all plastics are derived from crude oil. Recycling saves this expensive and diminishing source as well as the energy used in refining it. If plastics are not recycled they mostly end up in landfill sites. The plastics need to be collected, transported and sorted which uses energy and manpower and is therefore expensive....