AbstractFour α,ω‐diisocyanates (tetramethylene, hexamethylene, decamethylene, and eicosane) and six α,ω‐diacid chlorides (succinyl, adipyl, pimeloyl, sebacyl, dodecane, and docosane) were allowed to react with two types of nylon 66 yarn made from polymers of 14,800 and 21,000 number‐average molecular weights. The higher molecular weight yarn had a more ordered structure initially, as indicated by density measurements. Both diisocyanates and diacid chlorides crosslinked the yarn as shown by insolubility in 90 formic acid. Isocyanates were more efficient crosslinking reagents than diacid chlorides. Diacid chlorides caused simultaneous degradation of the yarn. The overall rate of reaction of the reagents with the yarn responded to temperature, reagent concentration, and time as expected for low molecular weight materials bearing the same functional groups. Catalysts had only a small effect on the rate of reaction. The reaction occurred in the less ordered regions of the yarn, as indicated by (1) a faster rate of reaction with the less ordered yarn, (2) the accelerating effect of swelling solvents on the rate, and (3) the reduction in extent of reaction with increase in molecular size of the reagent even though the reaction was not limited by diffusion. Both diisocyanates and diacid chlorides reduced the dyeability of yarn with acid dyes. Diacid chlorides increased the dyeability of yarn with basic dyes and diisocyanates decreased this d
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