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Summary
Water-soluble polymers (polyvinylpyrrolidone and polyethyleneoxide) can be cross-linked by irradiation when present in aqueous solutions. A study of the gelation dose versus concentration indicates little contribution from the indirect effect (due to energy absorbed in the water) in the range from 1 per cent to 65 per cent for polyvinylpyrrolidone K.35 and from 0·5 per cent to 10 per cent for polyethyleneoxide WSR.35.
The gelation dose is greatly modified by the presence of various small amounts of certain additives. The relationship between the degree of protection (i.e. the relative increase in gelation dose) and the additive concentration has been studied for various additives at different concentrations.
The following two different behaviours were found:
Type (a): the gelation dose increases with additive concentration.
Type (b): protection occurs up to a limiting concentration and is then unaffected by a further increase in additive concentration.
Values are given of the protection offered by a wide range of additives of the two types. Many additives of type (a) are distinguished by the presence of sulphur in their structure.
In the presence of oxygen the gelation dose is increased. This is not a true protection effect and is not affected by the additive.
A few comparisons can be made between the effect of some additives in polymer solutions and in protection experiments with mice.
Further investigations are in progress to study the fate of the protecting additives.