Reaction of hydroxyl radicals with polyethylene oxide in aqueous solution

In aqueous solutions the rate constant for OH + polyethylene oxide depends upon the concentration and upon the molecular weight of the polymer. If the rate is expressed as "k_M"(OH)(M), where (M) is the concentration of polymer in monomer units, "k_M" varies with x^-0.4 (x = degree of polymerization) in dilute solutions where polymer molecules are isolated from each other. In concentrated solutions ((M) ≳ 1 M) where polymer molecules essentially fill all of the solution, "k_M" is independent of x and is the same as the rate constant "k_M" for polymer of x = 3 or 4. For polymer of x = 3 or 4 "k_M" is independent of (M). Experimentally, "k_M" has been evaluated for polyethylene oxide polymers of different x's and concentrations in pulse radiolysis competition experiments using ferrocyanide and iodide as OH scavengers. An equation has also been developed from polymer solution theory and probability theory which gives the appropriate correlation of "k_M" with (M) and with x.