Chem424 - Synthetic Polymer Chemistry

Polyethers via S_N2 Reactions

Newcomers to polymer chemistry are surprised to learn that the most fundamental organic reaction in sophomore textbooks, the simple S_N2 displacement, is seldom used for polymerization. Of course, this reaction is usually accompanied by some side reactions such as elimination, so it less efficient than desired for step reaction polymerization because of the tyrrany of the Carothers equation. However, the yield is high enough in some special cases to be used for polymerization.

One trick is to prevent elimination reactions by using monomers lacking beta-hydrogens, as in this example for alpha, alpha'-dibromo-xylene.

There also many examples from the extensive work of Virgil Percek (Case Western Reserve Univ.) on liquid crystalline polymers, in which phase transfer catalysis was successfully used to minimize side reactions.

References:

• Crown Ethers and Phase Transfer Catalysis in Polymer Science, Mathias, L. J.; Carraher, C. E., eds., Plenum, 1984.
• Boileau, S., chapter 6 in New Methods for Polymer Synthesis, Mijs, W. J., ed., Plenum, 1992.
• Percek, V., in Phase Transfer Catalysis, New Chemsitry, Catalysts, and Applications, Starks, C. M., ed., ACS Symposium Series 1987, 326, 96-115.
• Percek, V.; Auman, B. C.Makromol. Chem. 1984, 185, 617-27.
• Percek, V.; Nava, H.; Rodriguez-Parada, J. M. Polym. Bull. 1984, 12, 261-8.
• Shaffer, T. D.; Percek, V. Makromol. Chem. 1986, 187, 1431-9.

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