In this paper, we present a novel post-polymerization modification strategy for the synthesis of highly functionalized PEO. Our approach utilizes a mild organocatalytic oxidative reaction pathway with carboxylic acids, which avoids unwanted PEO cleavage and allows for the attachment of a broad range of carboxylic acids, up to 5 mol% of repeat units. Unlike other methods, this approach does not impact the PEO structure, and the location of attachment is not limited to the end groups, thus enabling new types of applications. In our study, we demonstrated the potential of the modified PEO for drug delivery, as it contains an acetal unit that leads to steady hydrolysis and the release of carboxylic acids upon degradation in water.