Atom Transfer Radical Polymerization

Atom transfer radical polymerization (ATRP) is a way of forming carbon-carbon bonds in a controlled piece-by-piece fashion using a transition metal catalyst. ATRP is used to make polystyrene, poly(methyl methacrylate) and polyacrylamide.

The ATRP process relies on paired reduction-oxidation (redox) reactions between two species of copper:

• the activator, Cu⁺
  
• the deactivator, Cu²⁺
  

where the two catalysts exchange electrons back and forth.
Occasionally, one of the exchanges will spontaneously stop, called a radical termination, resulting in the accumulation of Cu²⁺. To keep the polymerization going, chemists must re-balance the system by compensating for the excess Cu²⁺. Simply adding more Cu⁺ to the system produces materials with high, sometimes toxic, levels of copper, up to 5,000 ppm. Such levels of copper are hard to remove using current industrial equipment. It has been found that reducing agents like sugars or vitamin C are highly effective in reducing the amount of copper catalyst used in ATRP reactions.

In a new study, Carnegie Mellon University chemists have found that they can use electricity from a battery to drive these ATRP reactions. Adding electricity capitalized on the redox reaction by moderating the transfer of electrons. This allowed them to compensate for the radical terminations and reduce the amount of copper needed to run ATRP. As a result the amount of copper in the system was reduced to 50 ppm, a 100-fold decrease.

Reference
Andrew J. D. Magenau, . Nicholas C. Strandwitz, . Armando Gennaro and Krzysztof Matyjaszewski. Electrochemically Mediated Atom Transfer Radical Polymerization. Science, 1 April 2011: Vol. 332 no. 6025 pp. 81-84 DOI: 10.1126/science.1202357

Further Reading:
Parts per Million (ppm)
Polymers and Polymerization
Oxidation and Reduction
Le Chatelier's Principle

Study Questions:

1. If 1kg of polystyrene contained 5000 ppm copper, what mass of copper would be present?
2. If 1kg of polyacrylamide contained 50 ppm copper, what mass of copper would be present?
   
3. Name the monomer that is used to produce each of the following polymers:
   
   • polystyrene
   • poly(methyl methacrylate)
   • polyacrylamide
4. Provide the structural formula for each of the monomers in question 1.
5. Draw the structure for each of the polymers listed in question 1.
6. In the reaction:
   Cu⁺ Cu²⁺ + e
   which species is
   • being oxidized?
   • being reduced?
   • the oxidant?
   • the reductant?
7. What is meant by each of the following terms:
   • oxidation
   • reduction
   • redox
     
   
   
8. Explain the statement "Adding electricity capitalized on the redox reaction by moderating the transfer of electrons. "
9. In the article, it is suggested that adding Cu⁺ or using electricity can moderate the transfer of electrons. Suggest another way that this might be accomplished.