Synthesis of Symmetric Fluorescently Labeled Poly(ethylene glycols) Using Phosphoramidites of Pyrenebutanol and Their Characterization by MALDI Mass Spectrometry

We report the synthesis and characterization of a series of poly(ethylene oxide) [PEO] polymers in which two pyrene groups are separated by a common EO 87 chain, and flanked by tails of varying EO x length. These polymers were prepared by reacting HO−EO 8 7 −OH ( M n = 3841, M w / M n = 1.01) with four different N, N -diisopropylphosphoramidites containing both pyrene (Py) and MeO−EO x − substituents. In this way, polymers of the form EO x −Py−EO 8 7 −Py−EO x (with MeO end groups) were obtained, with x = 2, 12, 17, and 47. These polymers are particularly useful for studying cyclization kinetics via pyrene excimer formation for two points labeled by pyrenes within the interior of a polymer chain. The polymers were characterized by NMR, size exclusion chromatography, and matrix-assisted laser desorption (MALDI) mass spectroscopy. The MALDI results were particularly informative since each of the oligomers of each of the components could be identified in each mass spectrum.