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Microwave-Induced Chain Transfer Polymerization of a Stimuli-Responsive Polymer and Determination of Its Critical Solution Temperature

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R. Freitag

Institute of Chemical and Biological Process Science, Chemistry Section, Faculty of Basic Science, Swiss Federal Institute of Technology, Lausanne, Switzerland

F. Fischer

Institute of Chemical and Biological Process Science, Chemistry Section, Faculty of Basic Science, Swiss Federal Institute of Technology, Lausanne, Switzerland; Hochschule Wallis, Life Technologies Institute, Biotechnology Unit, Sion 2, Switzerland

J. Chem. Educ., 2006, 83 (3), p 447

DOI: 10.1021/ed083p447

Publication Date (Web): March 1, 2006

Abstract

This experiment provides an introduction for undergraduate students to the concepts of living radical polymerization (oligomerization) and to stimuli-responsive materials, namely, those showing a critical solution temperature in aqueous solution. Students learn to polymerize and examine an intelligent polymer in a 8-hour, one-day laboratory period. The poly-N-isopropylacrylamide (PNIPAM) is a thermo-responsive polymer with a critical solution temperature (CST) of approximately 32 °C in pure water. Oligomeric PNIPAM (2000 g/mol) is telomerized with AIBN as initiator and 3-mercaptopropionic acid as chain transfer agent. The reactants are heated by microwave irradiation in a solvent-free process, employing a domestic microwave oven with 2.45 GHz magnetron frequency. The isolated telomer contains a single carboxylic function at one end of the polymer chain, allowing precise determination of the average molar mass by titration with NaOH solution and phenolphthalein as indicator. The CST phenomenon is easily detected by direct observation in daylight or by a temperature-programmed UV–vis spectrometer.