Aliphatic polyesters bearing pendant alkyne groups were successfully prepared by step-growth polymerization of different building blocks such as adipic acid and succinic acid in combination with an acetylene-based diol, 2-methyl-2-propargyl-1,3-propanediol, besides 1,4-butanediol and ethylene glycol. It was demonstrated that the alkyne groups survive the high reaction temperatures (200 degrees C) in the presence of a radical inhibitor. The alkyne loading has been tuned by the ratio of the different monomers used, up to 25 mol % of alkyne groups. Subsequently, the alkyne groups have been reacted with azides by the copper-catalyzed Huisgen 1,3-dipolar cycloaddition reaction, a popular type of "click" chemistry. "Click" reactions have been performed quantitatively in the presence of benzyl azide and azide-terminated poly(ethylene glycol), yielding brush copolymers in the latter case. Kinetic investigations about this click reaction have been performed by means of on-line Fourier transform mid-infrared spectroscopy, which was reported for the first time in the field of the click chemistry research. A whole range of functionalized polyesters, based on poly(ethylene succinate) and poly(butylene adipate), is available, the properties of which can be tailored by choosing the appropriate azide compound. (C) 2008 Wiley Periodicals, Inc.