Producing Polymers

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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.