1. Describe the components of an emulsion polymerization system on a macroscopic
level. Compare the pros and cons of emulsion polymerization as a process condition in
comparison to bulk and solution polymerization.
Solution:
The components of an emulsion polymerization on a macroscopic level including;
1. The monomer must be insoluble in water and polymerizable by free radicals
2. Water-soluble initiator
3. Water /or Dispersing medium
4. Surfactant /or Emulsifier
Pros and Cons of Emulsion polymerization as process condition comparison to Bulk and
Solution polymerization.
In bulk polymerization only the monomer (and possibly catalyst and initiator, but no
solvent) is fed into reactor. The monomer undergoes polymerization, at the end of which a
(nearly) solid mass is removed as the polymer product.
Bulk polymerization can be employed widely in the manufacture of condensation
polymers, where reactions are only mildly exothermic and viscosity is mostly low thus
enhancing ready mixing, heat transfer and bubble elimination.
Solution polymerization involves polymerization of a monomer in a solvent in which
both the monomer (reactant) and polymer (product) are soluble. Unlike Suspension
polymerization which is the polymerization in an aqueous medium with the monomer as
the dispersed phase. Consequently, the polymer resulting from such a system forms a solid
dispersed phase. Suspension is in oil phase where as in emulsion is in micelle.
Emulsion polymerization is similar to suspension polymerization but the initiator is
located in the aqueous phase (continuous phase) in contrast to the monomer (dispersed
phase) in suspension polymerization. Besides, in Emulsion polymerization the resulting
polymer particles are considerably smaller (about ten times smaller) than those in
suspension polymerization.
, Advantages and Disadvantages; /Pros & Cons;
Advantages:
a. Termination is controlled externally by the reason of the initiator’s insolubility in
the organic phase. The rate of arrival of radicals at the polymer particles is
established independently of propagation, by regulation of soap content, which sets
the number of micelle/polymer particles at 1014 to 1017 per ml of emulsion and by
the redox initiator concentration in the aqueous phase, which establishes the rate of
generation of radicals.
Thus, for example butadiene, which cannot economically polymerized
homogeneously by radical initiation (kt being very high compared to kp) is readily
polymerized by emulsion polymerization.
b. Because at least 50% of the volume is water, viscosity is always low and heat
removal rates are easily managed. It would be difficult to provoke runaway,
explosive polymerizations in emulsion polymerization.
c. In many cases the emulsion finally produced, ~ 0.1 µm polymer particles at around
50% volume fraction in water, is a product immediately applicable as coating, e.g.,
a paint or barrier coating layer: Poly (vinylidene chloride) on polyethylene.
Disadvantage:
The polymer will contain residues of the soap, which are hard to eliminate, even if the
polymer has been precipitated from the emulsion and washed. If the emulsion is used
directly as a coating, all the soap will be present.
level. Compare the pros and cons of emulsion polymerization as a process condition in
comparison to bulk and solution polymerization.
Solution:
The components of an emulsion polymerization on a macroscopic level including;
1. The monomer must be insoluble in water and polymerizable by free radicals
2. Water-soluble initiator
3. Water /or Dispersing medium
4. Surfactant /or Emulsifier
Pros and Cons of Emulsion polymerization as process condition comparison to Bulk and
Solution polymerization.
In bulk polymerization only the monomer (and possibly catalyst and initiator, but no
solvent) is fed into reactor. The monomer undergoes polymerization, at the end of which a
(nearly) solid mass is removed as the polymer product.
Bulk polymerization can be employed widely in the manufacture of condensation
polymers, where reactions are only mildly exothermic and viscosity is mostly low thus
enhancing ready mixing, heat transfer and bubble elimination.
Solution polymerization involves polymerization of a monomer in a solvent in which
both the monomer (reactant) and polymer (product) are soluble. Unlike Suspension
polymerization which is the polymerization in an aqueous medium with the monomer as
the dispersed phase. Consequently, the polymer resulting from such a system forms a solid
dispersed phase. Suspension is in oil phase where as in emulsion is in micelle.
Emulsion polymerization is similar to suspension polymerization but the initiator is
located in the aqueous phase (continuous phase) in contrast to the monomer (dispersed
phase) in suspension polymerization. Besides, in Emulsion polymerization the resulting
polymer particles are considerably smaller (about ten times smaller) than those in
suspension polymerization.
, Advantages and Disadvantages; /Pros & Cons;
Advantages:
a. Termination is controlled externally by the reason of the initiator’s insolubility in
the organic phase. The rate of arrival of radicals at the polymer particles is
established independently of propagation, by regulation of soap content, which sets
the number of micelle/polymer particles at 1014 to 1017 per ml of emulsion and by
the redox initiator concentration in the aqueous phase, which establishes the rate of
generation of radicals.
Thus, for example butadiene, which cannot economically polymerized
homogeneously by radical initiation (kt being very high compared to kp) is readily
polymerized by emulsion polymerization.
b. Because at least 50% of the volume is water, viscosity is always low and heat
removal rates are easily managed. It would be difficult to provoke runaway,
explosive polymerizations in emulsion polymerization.
c. In many cases the emulsion finally produced, ~ 0.1 µm polymer particles at around
50% volume fraction in water, is a product immediately applicable as coating, e.g.,
a paint or barrier coating layer: Poly (vinylidene chloride) on polyethylene.
Disadvantage:
The polymer will contain residues of the soap, which are hard to eliminate, even if the
polymer has been precipitated from the emulsion and washed. If the emulsion is used
directly as a coating, all the soap will be present.
