Network formation in polyurethanes based on triisocyanate and diethanolamine derivatives

The effect of the side chain length and the presence of charge in diols on gelation of polyurethane networks from diols based on diethanolamine deriva tives and tris(4-isocyanatophenyl) thiophosphate was studied. The samples h aving different initial ratios of the reactive hydroxy [OH] and isocyanate [NCO] groups (r(H) = [OH]/[NCO] ranging from 1.1 to 3) were investigated. T he number- and weight-average molecular weights in the pregel stage (M-n, M -w) together with the critical ratio of the reactive groups, r(H)(c), at wh ich gelation occurs, were determined, The experimental M-n and M-w values a re lower than the theoretical ones calculated for the ring-free case sugges ting that cyclization takes place. The Fraction of bonds lost in cycles, S, is 0.02-0.04 in the bulk state, increasing with increasing dilution and de creasing r(H). A pronounced decrease in r(H)(c), with dilution was found; w hile the length of the side chain of the diol has only a minor effect on th e decrease, the introduction of the charge (quaternization of the nitrogen) into the diol leads to a less pronounced decrease (lower extent of cycliza tion), The S values calculated from M-w and r(H)(c) were found to be always higher than S values calculated from M-n. A possible supramolecular struct ure is proposed for networks prepared from the uncharged diethanolamine-bas ed diols when prepared in the presence of diluent. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.