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PRODUCING POLYMERS

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POLYMERISATION REACTIONS

ADDITIONPOLYMERISATION CONDENSATIONPOLYMERISATION

Monomers are

added one by one toan active site in the

polymers growing

chain

Two different

monomers reacttogether and a small

molecule is

eliminated.

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ADDITION POLYMERISATION some facts:

Free-radical addition free radicals are

simple molecules that have an unpaired

electron.

The radical tries to pair its electron by

breaking the bond in a second molecule and

pairing with one of the electrons from the

bond. This leaves that molecule with an

unpaired electron.

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There are 3 steps to the addition

polymerisation reaction:

1.Initiation:

A free radical is produced by decomposing

the initiator molecule.

R O R/ R O + O R/

The oxygen atom of the free radical has an

unpaired electron ( ), is very unreactive and

exists for only a fraction of a second.

The free radical joins to the monomer.

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The pi bond of the carbon carbon double

bond is broken, the oxygen of the radical is

joined covalently with a carbon atom, leavingthe carbon atom at the other end of the

molecule short of one electron and it becomes

the radical.

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2.Propagation

During propagation the unpaired electrontransfers down the polymer chain, with

additional monomer units being added to

the chain.

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3.Termination

Termination can take place in two ways combination or disproportionation.

Combination occurs when 2 growing chains

join to form a single chain. The unpairedelectrons from each chain pair.

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During disproportionation other free

radicals combine with the growing chain. A

hydrogen atom is tripped from the chain

and a double bond is formed. This stops

chain growth.

Impurities in the reaction mixture usually

cause disproportionation. For this reasonpolymerisation reactions must be carried

out under very clean conditions.

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CONDENSATION POLYMERISATION some

facts:

Two monomers with functional groups that

react with each other join together, ususlly

with the elimination of a small molecule.

Co-polymers are usually formed during

condensation polymerisation.

Polyester and nylon are formed in this way.

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Synthesis of nylon

Carboxylic acid diamine

n = number of monomers units

The NH2 group reacts with the COOH group.

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Synthesis of polyester

The OH group reacts with the COOH group

to form an ester group.

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What should you be able to do?

explain how plastics (polymers) are

produced.

differentiate between addition and

condensation polymerisation.

distinguish between monomers andpolymers.