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MATERIALSdifference is thus as high as a factor of 3.5. Only when the conversion is higher than 85-90%, does the level of crosslinking agent drastically increase to more than 1 %.If the amount of cross-linking agent is adjusted so that the polymer chains are optimally cross-linked a t low conversions, the cross-linking density may be insufficient, or too high, for the short polymer chains at the end of the reaction. Larger or smaller quantities of cross-linking agent may indeed provide the necessary amount of cross-linker density at higher conversions but at lower conversions the amount is then either too low or too high.The only way to overcome the problem of varying the necessary amount of cross-linker is to use a mixture of a high-and low-reactivity cross-linking agent. The high-reactivity cross-linking agent acts preferentially at a low conversion and the low-reactivity cross-linking agent at higher conversions. By varying the ratio of the two, the cross-linking density can be adjusted over the whole range and network structures with good performance characteristics can be achieved. ~[I] P. K. Chatterjee: Ahsorbencv, Elsevier.

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