Five PEO-PPP rod-coil diblock polymers were synthesized and characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). By using a series of alkali chlorides as cation salts, relative cation affinities were studied. Different cation affinities and shifts in molecular weight distributions were found as a result of changing the cation type and size. Also, a study of lithium cationization resulted in determination of a recommended quantity of lithium to be used. Copyright © 2002 John Wiley & Sons, Ltd.