Diisocyanate Efficiency

Bernstein, D.I., Cartier, A., Cote, J., Malo, J.L., Boulet, L.P., Wanner, M., Milot, J., L Archeveque, J., Trudeau, C., and Lummus, Z., Diisocyanate antigen-simulated monocyte chemoattractant protein-1 synthesis has a greater test efficiency than specific antibodies for identification of diisocyanate asthma., Am. J. Respir. Crit. Care Med, 166,445, 2002. 

Bifunctional molecules such as diepoxides, diisocyanates, dianhydrides or bis(oxazoline)s have been shown to increase the molecular weight of PET [1,2] by reacting with its terminal groups. Triphenyl phosphite [3, 4], as well as diimidodiepoxides [5], have also proved to react efficiently with PET while promoting molecular weight enhancement. 

In the same study, it was shown that catalysis of hexane-1,6-diyl diisocyanate is carried out by acids having a pKa > 6, whereas stronger acids (pKa < 5) were less efficient catalysts. These results are compatible with the mechanism of general base catalysis with electrophilic addition of H20 postulated in Fig. 11.11. Hydration of isocyanate, thus, produces a carbamic acid, which spontaneously decomposes to the primary amine with loss of C02. 

Chain extenders Diols and diamines are generally used as chain extenders in PU industry and choice of chain extender influences elastomer properties considerably. The standard diol chain extender used for the synthesis of PU elastomer is 1,4-butane diol (BDO). Compared with a diol, better physical properties usually result when a diamine is employed as an extender. This is probably due to the introduction of urea linkages which enter into strong hydrogen bonded interactions. A diamine is usually chosen as the chain extender when a relatively unsymmetrical diisocyanate is employed. Diamines also function as efficient catalysts in addition to chain extenders. 

The most efficient intermediate layers are polyurethane adhesives or glues.175 In this case, the correct choice of molecular weight of the polyester and its ratio to diisocyanate is very important. The dependence of the adhesive strength on the molecular weight and the isocyanate-to-diol ratio is shown in Fig. 4.13. The best adhesion to metal is achieved when an intermediate layer based on low-molecular-weight polyester and at a ratio of NCO OH = 2.5 is used. 

Jahnisch et al. used an IMM falling-film microreactor for photochlorination of toluene-2,4-diisocyanate [38] (see also Chapter 4.4.3.3, page 161). As a result of efficient mass transfer and photon penetration, chlorine radicals were well distributed throughout the entire film volume, improving selectivity (side chain versus aromatic ring chlorination by radical versus electrophilic mechanism) and spacetime-based yields of l-chloromethyl-2,4-diisocyanatobenzene compared to those obtained using a conventional batch reactor. 

The time required for complete reaction is dependent on the reaction temperature, on the design of the phosgene inlet tube, on the efficiency of agitation, and on the rate of phosgene addition. It is important that the reaction be continued until practically all the hexamethylenediammonium chloride has disappeared. If unreacted amine salt is present, it has a tendency to sublime with the diisocyanate during distillation. 

Many papers and patents deal with incorporation of additives in the poly-(urethane-seq-butadiene)s to increase the condensation efficiency, to improve the processing, or to improve the properties of solid propellants. A processing aid, trialkylamine 2201 and also tetracycline 221), was shown to reduce the viscosity and increase the pot life of hydroxytelechelic polybutadiene/polyisocyanate systems. It has been shown that the cure of isophorone diisocyanate and hydroxytelechelic polybutadienes was not affected by the addition of the ammonium perchlorate propellant 222). Special modification of HTPBs have been referred to in Refs. 223 236>. 

Recently, Komiyama and co-workers have reported the preparation of novel cyclodextrin derived imprinted carbohydrates for the efficient recognition of cholesterol [34]. jS-Cyclodextrin was cross-linked in the presence of cholesterol using different diisocyanates as the cross-linking agents. These cyclodextrin matrices, after removal of the template, exhibited selective preference towards cholesterol compared to the non-templated cross-linked cyclodextrin. 

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-... 

In 2001, an efficient step-growth polycondensation approach, reminiscent of that used to prepare metal-metal-bonded polymers 217 and 218, was successfully developed to yield polyurethanes 225 with Mo2lt2 clusters in the backbone. " Well-characterized polymers with molecular weights of up to 136,000 (PDI = 3.1), which correspond to a number average of around 30 clusters per polymer chain, were obtained by means of this method. It involved treatment of a diol of the Mo2lt2 cluster with the diisocyanate OCN-R-NGO (R = aliphatic or aromatic spacer) in the presence of a tin catalyst. The unusual optical properties of organometallic clusters will drive applications-oriented work on these materials. " ... 

Very recently a rapid method for the preparation of effective polymer-supported isocyanate resins has been reported [31]. Gel-type isocyanate resins tvere generated from aminomethyl resins and inexpensive substrates as alternatives to the commercially available, expensive macroporous polystyrene isocyanate supports. Several isocyanates have been investigated phenyl diisocyanate (PDI) tvas found to be the most efficient. Aminomethyl resin was pre-swollen in NMP, mixed with 2 equiv. PDI, and irradiated at 100 °C for 5 min (Scheme 16.7). Filtration, washing with NMP and DCM and drying under vacuum furnished the corresponding isocyanate resin. The reactivity of this novel gel-type resin was better than that of commercially available methyl isocyanate resins and it was successfully used for purification of a small amide library [31]. 

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