Experimental confirmation of extent of reaction at the gel point in a polyisocyanurate

Abstract

SynopsisTheoretical equations were developed to relate the extent of reaction at the gel point for a system where three functional groups trimerize to a ring structure during the polymerization reaction. Specific relationships were developed for a difunctional monomer where the two functional groups are of unequal reactivity and for a mixture of difunctional and monofunctional monomer where all three functional groups are of unequal reactivity. These two cases were tested experimentally by determining the extent of reaction at the gel point for the system isocyanate reacting to form isocyanurate. In the case of 4,4'-diisocyanatophenylmethane (MDI), the extent of reaction a t gelation was determined experimentally to be 60%. When this data was analyzed according to the theory developed, a reactivity ratio of 2.38 was calculated for the rate of the first isocyanate group to react as compared to the second. Experiments were also performed with 2,4-toluene diisocyante, which gave a 72% conversion a t the gel point. The extents of reaction at the gel point for mixtures of MDI and phenyl isocyanate were also determined experimentally. An analysis according to the theory developed further supported the idea that all three isocyanate groups in this system have different reactivities. Theoretical relationships also were developed for a trifunctional isocyanate reacting to form isocyanurate. Experimentally, a crude MDI was used, and approximate relationships were used to analyze the results.

Network formation of polyurethanes due to side reactions

“…In the experimental system discussed below, the poly-(oxypropylene) diol contained a small admixture of the monofunctional component, so that = n1 + n2 = 1 and eq 8 is transformed into (9) The key quantities beyond the gel point are the extinction probabilities i>KL; i.e., uKL is the probability that the bond K-L has finite continuation. The extinction probabilities are given by the following expressions: (10) fHi = ^(on) = (s + WUnNlA8 + w) (11) un = Fu(vu, ulH) = [r + svm + tvji + uvn2 + wvuum + + ^ ( + 2 uvr + u>uIH + 2 xon)]/(r + s + 2f + 3u + 2w + 3x) (12) The sol is composed of units having no bonds with infinite continuation. The weight of these units, A, is given by the expression A = [NrMrüii + Ns AfsOnuiH + A^TMxon2 + NvMvvR + 1VwMwOh2Ojh + N -+ NRMiivm(n1 + n2oHI)] (13) where NK is the number of moles of the fragment K and MK is its molecular weight.…”

MM/RIM: RIM Composites Using Preplaced Reinforcement

“…A second measure of gel is the machine free pour time, often easily obtained during setup; it is about 65% of the handmix time. The shear experienced by the mixed components as they flow through the mats sharply reduces the gel time; thus the time available for dispensing is from [4][5][6][7][8][9][10][11][12] higher than D in Figure 5 are not cited. Finally, the demold time is given.…”

“…Thus the reaction is one which forms many lower molecular weight species, and these combine into a threedimensional network. The chemistry of cyclotrimerization has been examined by ourselves and others [4,5]. The function of added polyol is to act as a soft segment, to assist in conversion and to contribute some toughness to an otherwise brittle plastic.…”

Cure Conditions for Isocyanurate Polymers

“…Thus, bulk polymerizations, in INTRODUCTION I SOCYANURATE POLYMERS HAVE been shown to react experimentally in the laboratory to different extents depending on the functionality of the isocyanate. (1) For example, the conversion of a polymeric isocyanate of 2.61 weight-average functionality at gel was estimated to be 38%, whereas diphenylmethane diisocyanate (MDI) of functionality 2.0 was 50% converted.…”