TDI trimer

Crude TDI has an average functionality of more than 2 because it contains TDl-dimer, TDI-trimer, and carbodiimide-containing compounds. The NCO percent of crude TDI is about 40%, which is lower than pure TDI but is higher than crude MDI as well as TDI-based semiprepolymers, both of which have about 30% fi ee NCO. Accordingly, the kinds and amount of catalysts and surfactants for the one-shot, crude-TDI process are slightly different fi om those of TDI-based semiprepolymers. 

Mondur SH, thought to be a cresol blocked TDI trimer (Mobay)... 

Commercially available blocked isocyanates include Hylene MP or 4715 from Du Pont (now withdrawn), which is phenol-blocked MDI (Du Pont International S.A., Geneva, Switzerland) Mondur S, a phenol-blocked TDI adduct, Mondur SH, a cresol-blocked TDI trimer, and Experimental E-320-blocked isocyanate, a ketoxime-blocked tetraisocyanate, all from Mobay (Pittsburgh, Pennsylvania, USA) and Isonate 123P, which is s-caprolactam-blocked PAPI, from the Upjohn Company (Dow Chemical Europe, Horgen, Switzerland). These are shown in Fig. 8.9. Uniroyal also market a product. 

XXIII) Mondur SH—a cresol-blocked TDI trimer, presumably... 

Isocyanates are capable of co-reacting to form dimers, oligomers and polymers. For example, aromatic isocyanates will readily dimerize when heated, although the presence of a substituent ortho to the -NCO group reduces this tendency. For example, toluene diisocyanate (TDI) is less susceptible to dimer formation than diphenylmethane diisocyanate (MDI). The dimerization reaction is reversible, with dissociation being complete above 200 °C. It is unusual for aliphatic isocyanates to form dimers, but they will readily form trimers, as do aromatic isocyanates. The polymerization of aromatic isocyanates is known, but requires the use of metallic sodium in DMF. 

Figure 2. Trimerization of TDI. Effect of temperature. (TD1) = 100 mL [Catalyst VI — 7.4 mmol rate of catalyst addition, 20 min.

Buricus (201) and Nicholas and Gmitter (58) reported on TDI prepolymer-based isocyanurate foams prepared by trimerizing NCO-terminated jn-epolymers. TGA data (58) showed that there was no... 

A guinea pig inhalation model was developed by Karol (1983) to examine immune and pulmonary responses to TDI. Since that time, this model has been used by other investigators to examine immune and pulmonary responses to TDI and other chemical respiratory allergens such as diphenylmethane diisocyanate (MDI) (Karol and Thome, 1988), trimeric hexamethylene diisocyanate (Des-N) (Pauluhn and Eben, 1991), trimellitic anhydride (TMA) (Botham el al., 1988 Pauluhn and Eben,... 

Nicholas and Gmitter (58) studied the relative effectiveness of a number of trimerization catalysts (see Table I). Isocyanurate coatings based on TDI and HDI have been reported by Kubitza (59). In addition, Sandler (60) prepared polyisocyanurate adhesives from isocyanate-terminated prepolymers employing calcium naphthenate as a trimerization catalyst. 

The polymer is prepared by crosslinking p-CyD in DMSO with toluene 2,4-diisocyanate (TDI) in the presence of cholesterol as the template. In order to obtain homogeneous samples, the amount of TDI is kept small. Matrix-assisted laser desorption/ionization time-of-flight mass spectra (MALDI-TOFMS) are presented in Fig. 5.5. In the presence of the template (a), both the dimers of P-CyD (mass number (M) = 2000-3500) and its trimers (M = 4000-4500) are efficiently formed. In its absence (b), however, virtually all the products are monomeric P-CyDs (M = 1000-2000). The template enormously accelerates the bridging between two P-CyD molecules. Each of the signals in the spectra corresponds to different amount of substitution by TDI. These analyses clearly show that dimeric P-CyDs (the binding sites for choles-... 

As distinct from MDI, the monomers of HDI and the TDI isomers, as well as MIC, are volatile, but may still be present in workroom air as nonvolatile dimers, trimers or prepolymersPrepolymers of the volatile diisocyanates, such as biuret, allofanat, and isocyanurate adducts, exhibit substantially lower vapor pressures than the diisocyanates, reducing the gaseous phase exposure levels. Highly reactive isocyanates in workroom air may exist as vapors, aerosols, or in mixed phases, rendering sampling of isocyanates in workroom air a complicated task. 

PEO and PPO, are mixed to create Type III segmented polyurethanes, three different diblock sequences of equal probability must be obtained PEO-PEO, PEO-PPO, and PPO-PPO are the principal species. The same principles that govern the formation of l-,3-,5-,-7... unit combination of diisocyanates and diamines in the hard segment, also predict that the reaction product of 2 mol of a, co diol with 1 mol of diisocyanate after Step 1 of the three-step process (Figure 2) will consist mostly of the monomer (the diol), some of the desired trimer (diol -TDI-diol), but also some of the pentamer (diol-TDI-diol-TDI-diol), etc. 

Because of the high cross-Knk density of polyisocyanurates, the resultant foam tends to be brittle. Consequently, there has been a move toward making polyisocyanurate-polyurethance combinations. For example, the isocyanate trimerization reaction has been carried out with isocyanate end-capped TDI-based prepolymers to make isocyanurate-containing polyurethane foams. Isocyanate trimerization in the... 

In the equation a trimer is shown, but more complicated ring structures will also be formed, due to reaction of some of the three unreacted trimer -NCO groups with further TDI. 

On the other hand, when two glutamic acids were attached to the dye molecules, the possibility arose of connecting two or more nanoparticles with rylene dyes. Thus, the designed TDI 38 with two dicarboxylic acid anchors at the imide nitrogen atoms was synthesized by the same procedure as described above. The dianhydride 43 was obtained by complete saponification of TDI 42 [7]. Further imidization of 43 and p-glutamic acid afforded TDI 38 [58] (Scheme 10). The complexation between TDI 38 and QDs led to the formation of QD dimers and trimers, for which energy transfer from the QDs to the TDI bridge was observed. 

The principal commercial aromatic isocyanates are toluene diisocyanate (TDI), polymeric isocyanate (PMDI), and its coproduct (MDI), but some specialty aromatic isocyanates and some aliphatic diisocyanates are also available. The latter are used in the manufacture of color stable pol5uirethanes. TDI is mainly produced as a 80 20 mixture of the 2,4- and the 2,6-isomers, but a 65 35 mixture of the same isomers, pure 2,4-TDI and a crude partially trimerized product, are also available. PMDI is a mixture of the MDI isomers and their higher oligomers, and MDI is mainly the 4,4 -diisocyanate. The principal commercially available isocyanates are listed in Table 2. 

Aromatic triisocyanates as cross-linkers are more readily obtained by trimer-izing 2,4-TDI. In this reaction the more reactive isocyanate group in the 4-position undergoes trimerization to produce a triisocyanate (20). 

Diisocyanates are commonly used with either diols or a mixture of diols and polyols. When diols are exclusively used and the trimerization reaction is minimized, the polyurethane is substantially linear, but it becomes increasingly three-dimensional with increasing levels of polyol or with trimerization of the diisocyanate. The trimerization reaction and the use of polyols enable thermoset polyurethanes. Common diisocyanates include toluene diisocyanate (TDl), methylene diphenyl diisocyanate (MDl), naphthalene diisocyanate (NDl), and hexamethylene diisocyanate (HDl). TDI is prepared by the nitration of toluene to give a mixture of mainly 2,4- and 2,6-dinitrotoluene, followed by reduction and reaction with phosgene. The isomers are typically not separated and are used as a mixture. 

The high selectivity for dimer formation observed with trialkylphosphines can be explained by a stepwise mechanismThe general base catalysis of oligomerization of isocyanates involves the dimeric species as intermediates in the formation of the more stable isocyanate trimers (isocyanurates). Steric effects also play a role in the dimerization of isocyanates because o-tolyl isocyanate does not dimerize. This fact is utilized in the selective dimerization of 2,4-TDI 7, using a polymeric imidazole catalyst. In this reaction only the non-hindered isocyanate group participates to form the [2-1-2] cyclodimer 8. 

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