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Chain -Growth Polymerization of Styrene and Methyl Methacrylate

Polymer - a very large molecule composed of smaller repeating units (monomers) bonded together

Addition Polymer - result from addition of one molecule at a time to a growing polymer chain, usually by

a reactive intermediate (e.g., cation, anion, radical) at growing end

H2C CH

G

Rad +H2C CH

G

H2C CHG

Rad

n

H2C CH

G

H2C CH

G

H2C CH

G

RadH2C CH

G

H2C

HC

G

Rad

H2C CHG

n

n= degree of polymerization (chain length) number of repeating units

RepeatUnit

Emulsion Polymerization: polymerization process which takes place in a colloidal dispersion of two

immiscible liquids (monomer and solvent) in the presence of an emulsifying agent (which allows forpartial mixing of the two).

Solution Polymerization: polymerization process carried out in water without the use of an emulsifying

agent so as to produce the polymer in small granules.

Bulk Polymerization: polymerization carried out without the use of a solvent.

Polymerization Initiator: A compound that disassociates to produce free radicals which begin a

polymerization reaction.

Scheme A: (Emulsion polymerization of styrene)

H2C CH

Styrene

RadH2C

CH

Rad

H2C CH

+

H3CCH

H2

CCH

H2C CH

Polystyrene (PS)n

Mechanism:Step 1: Initation (disassociation of peroxydisulfate)

Step 2: Free-radical addition to monomer and subsequent additions

Step 3: Termination

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Procedure: (Begin this part first.)

1) In a 125 mL flask, add 5 g of styrene. Add 50 mL of water, 0.1 g of sodium peroxydisulfate, 0.35 g of

sodium laurylsulfate and a stir bar.2) Wrap the top of the flask with parafilm and warm the mixture for 2 h with vigorous stirring.

3) Add 10 mL of saturated alum to the mixture, boil gently for 2 min. and collect the polystyrene

product on a filter.4) Transfer the sample to a 25 mL beaker, add 5 mL of methanol, swirl the mixture for 30 sec and

decant. Repeat this procedure until the sample is no longer sticky, collect the product on a filter anddry (with the vacuum on).

5) Weigh the product and obtain an IR spectrum as follows: dissolve a few mg of sample in about 1 mLof tetrahydrofuran in a small beaker and place the solution dropwise on a microscope slide. Allow the

solvent to evaporate, carefully remove the resulting clear film with a razor blade and pass the beam

through the film.

Scheme B: (Bulk polymerization of methyl methacrylate)

H2C C

CH3

CO2Me

Initiator H2C C

CH3

C

H2C C

CH3

C

H2C C

CH3

C

H2C

OMeO

OMeO

OMeO

Mechanism:

Step 1: Initiation (disassociation of t-butylperoxybenzoate as well as breakdown of benzoate radical to

CO2and phenyl radical)

Step 2: Free-radical addition to monomer and subsequent additionsStep 3: Termination

Procedure:1) To 10 mL of methyl methacrylate in a test tube, add 5 drops of t-butylperoxybenzoate and mix.

2) Place the tube in a hot water bath and heat until the contents begin to boil. With short-wave radiation,

hold an ultraviolet lamp above the top of the tube so that the light shines directly onto the surface ofthe solution and continue boiling until the solution becomes a solid. Repeating exposure to UV lightmay be necessary.

3) Wrap the tube in a paper towel and CAUTIOUSLYbreak it up. Carefully remove any glass that may

stick to the polymer using forceps.

4) Weigh the sample and obtain an IR spectrum as with polystyrene using acetone as the solvent.