The Notes for
Polymer and Coatings Science-
Chapter Two- part one

Chapter Two (which I believe corresponds to the start of material that will be on the second test) opens with a discussion of the polypropylene business. Quite of a few of the ideas here were introduced in Chapter One (Ziegler Natta, etc.) but there is more detail here.

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.

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: 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:
  1. Bulk
  2. Solution
  3. Suspension
  4. Emulsion
and the following six concerns:
  1. Initiation
  2. Propagation
  3. Termination
  4. Molecular Weight
  5. Rate (kinetics)
  6. 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.

Bulk addition polymerization is a homogeneous process which uses an organic initiator. Two possibilities: The above probably implies that polyvinylidine chloride precipitates out of the solution of vinylidine chloride monomer when it reaches a certain molecular weight, but that polystyrene is soluble in styrene to infinite molecular weight.

If the polymer is soluble in the monomer, then some physical changes occur with increasing molecular weight (e.g., viscosity, etc.)

If the polymer is insoluble in the monomer, the rate of initiation is proportional to the monomer concentration, the initiator concentration, and the inverse square of ???K over t???

The higher the temperature, the lower the molecular weight of the polymer produced. It is thought that the notes here allude to the idea that at higher temperatures, the initiator decomposes to form radicals at a faster rate, then We can have continuous polymerization at very low temperatures if we use light to convert the initiator molecules to radicals (which will start the polymerization.)

Bulk polymerization has a built in hazard. The thermal conductivity of monomers and polymers is low, and as the viscosity builds up, the ability for heat transfer via convection is substantially diminished. If the heat energy cannot be dissipated, temperature rises, and at higher temperatures the reaction is going to go faster, so this is a positive feedback loop with disastrous consequences.

For bulk polymerization, removal of unreacted monomer can be a problem. This is a large concern if your safe polymer was prepared from monomers which are toxic. The Federal Drug Administration (FDA) puts limits on how much monomer can be present in a polymer system used for food containment.

Solution Polymerization- If both the monomer and the polymer system are soluble in the solution (i.e., no polymer precipitation), then as the polymerization occurs, the viscosity of the solution increases. The rate (of polymerization?) will decrease with time. The rate (of polymerization?) is proportional to monomer concentration, initiator concentration, and the inverse square of (K multiplied by t.)

Now, for solution polymerization where the polymer is insoluble in the solution above a certain molecular weight (i.e., the polymer precipitates out at that molecule weight) then the viscosity is more likely to remain fairly constant. Dimerization termination is more likely, and the rate of chain transfer is faster. Heat effects are much better (I think this means that the problems of heat transfer are not as much of a problem.)

Solution polymerization and bulk polymerization are carried out at the highest temperature (i.e, the highest temperature within reason- you don't want decomposition of monomer or polymer. I don't think runaway reaction is a problem) because condensation reactions can occur on the timescale of hours or days.

For some condensation polymerizations, you can drive the condensation by-product from the reaction by azeotrope.

Suspension polymerization is used only in free radical type processes. The monomer is mechanically dispersed in a media, usually water. There are cases where an organic media is used in which neither the polymer nor the monomer are soluble in the organic media. For suspension polymerization, there are two phases, water and organic, and the starting point may be 10 parts of the former, and 1 part of the latter. The initiator used can be water soluble or organic soluble [benzoyl peroxide, AIBN, or (NH4)2(SxO4)y.] Usually the initiator is organic soluble.
  1. There are two separate phases throughout the whole process.
  2. The droplets must be kept far apart.
      this requires agitation: consistent, efficient, and controlled. A suspending agent can be used. Poly(vinyl alcohol) dissolved in the aqueous phase is a typical suspending agent.
  3. The rate of suspension polymerization is similar to the rate of bulk polymerization, but the heat transfer is much better. For suspension polymerization, initiation, propogation, and termination take place inside the droplet.
    • examples include the polymerization of methyl methacrylate, and vinyl chloride.
    • The solution polymerization of butadiene, isobutylene and isoprene require a pressure system.
    • the media to monomer ratio is 10:1. Is this wt/vol, wt/wt, or vol/vol?? In an industrial setting it may be easier to combine chemical feedstocks on a per volume basis. Ask Dr. Stoffer.
    • Particle size is affect by the following four factors:
      1. stirring rate
      2. ratio of reactants
      3. suspension agent
      4. temperature
    • The plant operator must control temperature, and the particle size (of the growing polymer mass in the bubble.) If the particle size gets to large, the particle will absorb too much heat. This probably relates to the idea that as you increase the volume of a sphere, the ratio of surface area to volume decreases, and this ratio relates to heat transfer. Particle size may be 0.01 to 0.5 cm, or as low as 1 micron.
A suspension agent is a material that gives a surface activation that keeps droplets from become larger (droplets coming together to form larger droplets is called coalescence.)
Suspension polymerization is similar to bulk polyerization, and it could be considered "bulk polymerization within a droplet." The speed at which the reaction takes place for a given temperature is the same, and just as for bulk polymerization, the kinetics or rates are proportional to monomer concentration.

There is efficient heat transfer with speed or bulk process.

Recovery of product by mechanical separation (i.e, filtration, washing) is a lot cheaper than thermo distillation. (this sentence sort of doesn't make sense.)

The properties of the polymer are similar to those of the same polymer made by a bulk polymerization.

 Limitations of suspension polymerization-
  1. It only applies to free radical process
  2. ionic catalysts don't work because they compete with water (huh??)
  3. agitation is critical because as the viscosity within the bead rises, the reaction rate increases suddenly ( Tromsdoiff effect.) This leads to a surge in heat generation which does not usually occur in solution or emulsion polymerization.
Things to consider for Emulsion polymerization-
  1. monomer
  2. media (water)
  3. soap (also referred to as the emulsifier, or the surfactant)
      three different names for the same thing
  4. minor amount of mechanical stirring
  5. initiator
  6. stabilizer (suspension agent)
The basic difference between the suspension process and the emulsion process is the surfactant.

For an emulsion polymerization process the small droplets are stabilized by the surfactant.

The initiator can be either in the aqueous or the organic phase. This is a difference between emulsion and suspension polymerization.

Initially, a small amount of agitation is needed. The surfactant is in the form of micelles. Below is an illustration of a micelle, and for our purposes, this miscelle is in water. The hydrophilic (polar) end groups lineup on the outside and the hydrophobic ends are placed on the inside.

Note that this picture is a two dimensional cutaway, and that an actual micelle is the spherical 3-D equivalent.




Below is a graph of surface tension as a function of micelle concentration. At a certain concentration, increases to the concentration result in a sudden increase in the slope of the function.




Example of a molecule that forms a micelle: 
                                                                     O
                                                                     ||  -  +
CH -CH -CH -CH -CH -CH -CH -CH -CH -CH -CH -CH -CH -CH -CH -CH -CH - C  -O  Na
  3   2   2   2   2   2   2   2   2   2   2   2   2   2   2   2   2 

<----------------------------------------------------------------->  <--------->
hydrophobic                                                          hydrophilic


If monomer is added to a micellear dispersion, most of the monomer remains as large droplets, but some of it dissolves in the micelles. Since the monomer droplets are smaller, the micelles present much greater surface area than the monomer droplets. Consequently, when free radicals are generated in the aqueous phase, the micelles capture most of them.

Surface Area- The combined micellear surface area is larger than the combined micellear surface area of the monomer droplets. After a few percent conversion of monomer to polymer, the system consists of:
  1. stabilized, monomer-swollen polymer particles rather than micelles
  2. monomer which is still mainly in droplets, although it constantly changes as the polymerization continues
After 30% conversion of monomer to polymer, there is a decrease in (???the number of???) monomer droplets.
At 78- 80% conversion, monomer concentration poses less of an effect, and the reaction goes faster.


The monomer consumed by the polymerization in the micelle is replaced as more monomer diffuses from the aqueous solution into the micelle. As monomer leaves the aqueous solution, more monomer from monomer drops leaves the monomer droplets and thus maintains a steady concentration of monomer in the aqueous solution. To sum this up, here is the "life cycle" of a monomer molecule.
  1. The monomer is put in the aqueous media and it goes into a monomer droplet. There is too much monomer in the media for all the monomer to be homogeneously dispersed in the media because the monomer is minimally soluble.
  2. The monomer eventually leaves the droplet and goes into the media. A drawing in the notes implies that the monomer forms a complex with an SO4 radical.
  3. The monomer diffuses into the micelle.
  4. The monomer becomes part of the polymer.
The first free radical to enter a monomer swollen micelle starts the polymerization. The second free radical to enter the micelle terminates the polymerization. When the third free radical enters the micelle, the process is repeated. As this process repeats, the micelle becomes larger and larger. The micelles are disrupted to form particles of polymer swollen with monomer which are stabilized by soap molecules around the periphery.

Polymer product is isolated by 'breaking' the latex, usually by the addition of an acid which converts 
            O                                  O
            ||                                 ||
the soap, - C - O(-) (+)Na, to a fatty acid, - C - OH.


Five types of surfactants There are five categories of wetting agents (i.e., surfactants) used by the coatings industry.
  1. Anionic wetting agents 
              O
  +  -    ||
NH    O - C - CH  - CH  - CH  - ( CH ) - CH - CH
  4             2     2     2       2 x    2    3
  2. Cationic wetting agents 
      -  +    
Cl    NH  - CH  - CH  - CH  - ( CH ) - CH - CH
        3     2     2     2       2 x    2    3
  3. Electroneutral wetting agents 
                                   O
                       +  -    ||
CH  - ( CH )  - CH - NH    O - C - CH  - ( CH ) - CH
  3       2 x     2    3             2       2 x    3
  4. Amphoteric wetting agents 
                               O
                           || 
H N -CH  - (CH )  - CH  -  C  - OH
 2     2      2 x     2

base side                acid side
      It didn't say so in the notes, but it should make sense to you that in a polar solution, the active hydrogen of the carboxylic acid group of one molecule will protonate the amine base of another, and then there will be a (+)(-) interaction between the two.


  5. Nonionic wetting agents 
    HO-CH -CH -O-(CH -CH O-)-CH -CH -(-CH ) -CH -CH -CH
     2   2      2   2      2   2     2 x   2   2   3




Last Update- May 27, 1995- wld