Unusual kinetics of poly(ethylene glycol) oxidation with cerium(IV) ions in sulfuric acid medium and implications for copolymer synthesis.

The cerium(IV)-alcohol couple in an acidic medium is an example of a redox system capable of initiating free radical polymerization. When the alcohol has a polymeric nature, the outcome of such a process is a block copolymer, a member of a class of compounds possessing many useful properties. The most common polymer with a terminal -OH group is poly(ethylene glycol) (PEG); however, the detailed mechanism of its reaction with cerium(IV) remains underexplored. In this paper, we report our findings for this reaction based on spectrophotometric measurements and kinetic modeling. We find that both the reaction order and the net rate constant for the oxidation process depend strongly on the nature of the acidic medium used. In order to account for the experimental observations, we postulate that protonation of PEG decreases its affinity for some of the cerium(IV)-sulfate complexes formed in the system.