mPEG‐aldehydes and activated mPEG‐carboxylic acids on which the polymer and the reactive functional group are separated by aliphatic chains of different lengths, are well known reagents of widespread application in PEGylation technology. The syntheses of these functional polymers are not easy and usually the preparation of each of these compounds requires a very specific set of reagents and experimental conditions. In fact, a general method for their preparation is, still nowadays, unavailable. In this work a simple synthetic method is developed for preparation of mPEG‐aldehydes and carboxylic acids with excellent yields. The key step of the method involves a substitution reaction of mPEG‐mesylate with mono‐alkoxides of symmetrical diols to afford hydroxyl‐terminated polymers, which are converted to the aldehydes and acids by mild oxidation reactions.
