Dispersion Polymerization

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(1) Dispersion Polymerization using Supercritical CO2
Cross-linked polymers can be synthesised in scCO2 in the form of regular microspheres in the size range 0.2-5 micrometres (see electron micrograph on right) by dispersion polymerisation.  No organic solvents are used in this process, and the carbon dioxide can be separated very simply to leave a dry, solvent-free product (A.I. Cooper et al., Macromolecules, 1999 32, 2156).  Cross-linked polymer beads in this size range are important for applications such as solid phase synthesis, chromatography, and molecular imprinting.

 

The DeSimone group in North Carolina was the initial pioneer in this area (see Science 1994 265, 356).  Other groups studying dispersion polymerization in scCO2 include the Howdle group in Nottingham, the Beckman group in Pittsburgh, and the Johnston group in Texas. 

 

More Articles on Dispersion Polymerisation using scCO2:

(1)  J.L Kendall, D.A. Canelas, J.L. Young and J.M. DeSimone, Chem. Rev. 1999 99, 543 (Review)

(2)  M.Z. Yates, G. Li, J.J. Shim, S. Maniar, K.P. Johnston, K.T. Lim and S. Webber, Macromolecules 1999 32, 1108

(3)  P. Christian, S.M. Howdle and D.J. Irvine, Macromolecules 2000 33, 237

(4)  H. Shiho and J.M. DeSimone, Macromolecules, 2001 34, 1198

(5)  A.I. Cooper, W.P. Hems, and A.B. Holmes, Macromol. Rapid. Commun. 1998 19, 353

(6)  W.P. Hems, T.-M. Yong, J.L.M. van Nunen, A.I. Cooper, A.B. Holmes and D.A. Griffin, J. Mater. Chem. 1999 9, 1403

(2) Dispersion Polymerization using Hydrofluorocarbon Solvents

CO2 is a good solvent for dispersion polymerization but there are two main drawbacks:

 

(i) High pressures (150-350 bar) are required

(ii) Expensive fluorinated steric stabilizers are involved

 

We have studied the use of 1,1,1,2-tetrafluoroethane (R134a) as a solvent for polymerization (C.D. Wood et al., Macromolecules, 2002 35, 6453).  Although R134a is more expensive than CO2, but it is non-toxic, non-flammable, and can be used in the liquid state at much lower pressures (10-30 bar).  We have synthesized uniform cross-linked polymer microspheres by dispersion polymerization in this solvent.  Future goals include the synthesis of linear polymers and the use of less expensive hydrocarbon stabilizers.