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

Abstract

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.

Periodate Oxidation of Peg–600, an Essential Pharmaceutical Polymer

“…Conversion to 2,4dinitrophenyldrazones further established the formation of aldehydes. Nature of products are in the same order that reported by Szymański JK et al [24]. Though the technical name of these substrates is 'polyethylene oxides', but commonly called as polyethylene glycols because the terminal-OH groups present on these displayan ample effect on physical properties and also on chemical properties [43].…”

“…Catalytic amounts of Mn/Ce composite oxide direct the oxidation of PEG to a radical mechanism [29]. Similarly, the involvement of free radicals was proposed using Ce(IV) oxidant in sulphuric acid medium in spite of the incomplete understanding of mechanism [24]. Poly(oxyethylene)-dicarboxylic acids were resulted in high concentrations in the room temperature oxidation of PEGs by Jone's reagent [30,31] proposed two different stages in the uncatalyzed oxidation of PEG by permanganate and also studied the Ruthenium (III) influence.…”

“…Literature collection shows that kinetics of oxidation reactions involving N-halo oxidants [13][14][15][16][17][18][19][20][21] and inorganic oxidants [22,23] were well studied. Similarly, researchers are interested in the study of oxidation of various substituted alcohols [13,14,21] including polyethylene glycols and especially, ceric (IV) ions [24,25] and Fenton [26][27][28] were the best used oxidants. Catalytic amounts of Mn/Ce composite oxide direct the oxidation of PEG to a radical mechanism [29].…”

Kinetics and mechanistic aspects on electron‐transfer process for permanganate oxidation of poly(ethylene glycol) in aqueous acidic solutions in the presence and absence of Ru(III) catalyst

“…The kinetics and mechanisms of oxidation of natural polymers such as polysaccharides by the permanganate ion as a multivalent oxidant in both aqueous acidic and alkaline solutions was the subject of many investigators; a little attention has been paid to the oxidation of synthetic polymers such as poly(vinyl alcohol) . Indeed, the oxidation of PEG by the cerium(IV) ion as one‐equivalent oxidant has been studied elsewhere . It is pointed out that the oxidation process of this latter redox reaction was proceeding via a free‐radical intervention mechanism without formation of stable intermediate complexes.…”

“…5 Indeed, the oxidation of PEG by the cerium(IV) ion as one-equivalent oxidant has been studied elsewhere. 6,7 It is pointed out that the oxidation process of this latter redox reaction was proceeding via a free-radical intervention mechanism without formation of stable intermediate complexes. However, a lack of information on the nature of the electron-transfer process and transition state in the ratedetermining step still not complete.…”