Practical Aspects of How To Make An Addition Polymer
Bulk Polymerization
The bulk addition polymerization is the simplest of all polymerization processes. A bulk addition polymerization is a homogeneous system with an organic initiator.
If the polymer is insoluble in monomer, then initiation, propagation, and termination might happen in the monomer phase.
If the polymer is soluble in the monomer, then the concentration of monomer decreases continuously and the viscosity changes.
Solution Polymerization
The main advantage of a diluent (either water or an organic solvent) is to take up the heat of polymerization. For solution polymerizations, there are two possibilities:
monomer is soluble and the polymer is soluble in the diluent:
example: polystyrene in toluene
monomer is soluble and the polymer is insoluble in the diluent:
example: acrylonitrile in chloroform
The advantage of solution polymerization over bulk polymerization is better heat control; the disadvantage solution polymerization is the removal of the diluent from the polymer. This requires a distillation, and that costs an appreciable amount of money.
Suspension Polymerization
(Pearl Polymerization) If the monomer is insoluble in water, bulk polymerization can be carried out in suspended droplets, i.e., monomer is mechanically dispersed. The water phase becomes the heat transfer medium. Since it (the water??) is a continuous phase, viscosity changes very little as the monomer converts to polymer, so the heat transfer is very good. In this system, the monomer must be either 1) insoluble in water or 2) only slightly soluble in water, so that when it polymerizes it becomes insoluble in water.
The behavior inside the droplets is very much like the behavior of bulk polymerization, but since the droplets are only 10 to 1000 microns in diameter, more rapid reaction rates can be tolerated (than would be the case for bulk polymerization) without boiling the monomer.
The advantages are better heat control of the reaction, and separation is much easier than in solution polymerization. The disadvantage is that few monomers are water soluble.
Emulsion Polymerization
The "ingredients" for an emulsion polymerization include 1) a water soluble initiator, 2) a chemical emulsifier, and 3) a monomer that is only slightly soluble in water, or completely insoluble. (author notes: I think the words "completely immiscible" are more appropriate since I assume that in order to react, the monomer has to be a liquid.)
The two differences between emulsion and suspension polymerization are: 1) that a suspension polymerization is a mechanical process, and must have a stabilizing agent until the droplets are far apart, and 2) the emulsion polymerization is a chemical process which requires a surfactant to make the monomer "emulsify."
Disadvantage- the surfactant is a soap and it contaminates the polymer.
Advantage- better heat control; the size of the emulsion polymer is usually 0.05 to 5 microns, and the size of the droplets is usually in the 10- 1000 micron diameter range.
Water-soluble initiators are used rather than monomer-soluble initiators. The end product is usually a stable latex--an emulsion of polymer in water rather than a filterable suspension.
The notes go on to give more detail about the four types of polymerization:
Bulk
Solution
Suspension
Emulsion
and the following six concerns:
Initiation
Propagation
Termination
Molecular Weight
Rate (kinetics)
Heat effects (thermodynamics)
Addition polymerizations are usually carried out bulk and solution polymerizations.
Condensation polymerizations are carried out mostly without solvents. The polyerization of polyethylene terephthalate (PET), the plastic used for 2 liter soda bottles is an example of a bulk condensation reaction.