Abstract
The rate of oxidation (by dissolved oxygen) of a number of weakly basic ion-exchange resins has been determined at 80°C. Polystyrene-based systems with only tertiary or only secondary amino groups are the most resistant to oxidation. The presence of a mixture of primary, secondary and tertiary amino groups or of hydroxyalkylamino groups increases the rates of oxidation by about a factor of five. The more basic high capacity allylamine-type resins oxidize even faster and, within this series, the higher the basicity the greater the rate of oxidation. Also within this series, the greater the amount of residual unsaturation — from the presence of pendant allyl groups — the greater the rate of oxidation. The oxidation occurs by a free radical chain process but the chains are very short and therefore the oxidation cannot be significantly inhibited by antioxidants. Certain polymeric backbone structures favour resins which are more resistant to oxidation than allylamine systems. Of the former, only those with polyether backbones are suitable for thermally regenerable ion-exchange systems. Resins with a polyether backbone were prepared by crosslinking polyepichlorohydrin and aminating with secondary amines. The predicted capacities for thermally regenerable systems made by combining these oxygen-resistant resins with polyacrylic acid are comparable with those for the polyallylamine resin systems.
Published Version
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