Toluene diisocyanate polymerization

Chemoenzymatic synthesis of alkyds (oil-based polyester resins) was demonstrated. PPL-catalyzed transesterification of triglycerides with an excess of 1,4-cyclohexanedimethanol mainly produced 2-monoglycerides, followed by thermal polymerization with phthalic anhydride to give the alkyd resins with molecular weight of several thousands. The reaction of the enzymatically obtained alcoholysis product with toluene diisocyanate produced the alkyd-urethane. 

Commonly used isocyanates are toluene diisocyanate, methylene diphenyl isocyanate, and polymeric isocyanates. Polyols used are macroglycols based on either polyester or polyether. The former [polyethylene phthalate) or polyethylene 1,6-hexanedioate)] have hydroxyl groups that are free to react with the isocyanate. Most flexible foam is made from 80/20 toluene diisocyanate (which refers to the ratio of 2,4-toluene diisocyanate to 2,6-toluene diisocyanate). High-resilience foam contains about 80% 80/20 toluene diisocyanate and 20% poly(methylene diphenyl isocyanate), while semi-flexible foam is almost always 100% poly(methylene diphenyl isocyanate). Much of the latter reacts by trimerization to form isocyanurate rings. 

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. 

We have prepared and characterized three linear isosorbide containing polyurethanes with toluene diisocyanate (TDI), 4,4 -diphenylmethane diisocyanate (MDI), and 1,6-hexamethylene diisocyanate (HMDI) P(I-TDI), P(I-MDI), and P(I-HMDI). These polyurethanes have been synthesized as described in the experimental section by solution polymerization of isosorbide with the corresponding diisocyanate in dimethylacetamide using dibutyl-tin dilaurate as the catalyst at 75 C for 24 hours. All polymers have been isolated in quantitative yield by precipitation in methanol or water (5). 

Cellulose triacetate segments Cellulose triacetate, supplied by Eastman Kodak Company of Kingsport, TN, was depolymerized in accordance with a method by Steinmann (15), and this was NCO capped by reaction with toluene diisocyanate as reported previously (14). A CTA segment with an average degree of polymerization of 12 (corresponding to an M of... 

Toluene diisocyanates are reactive molecules that combine readily with nucleophiles, and as such have a propensity to react with proteins at the site of application to animals, in other tissues and with plasma (Kennedy et al., 1994). They are hydrolysed in aqueous media to the corresponding diamines, which can react with unchanged toluene diisocyanates to form polymeric ureas (Chadwick Cleveland, 1981 Ulrich, 1983). 

Major uses of aniline include the manufacture of / ,//-methylene diphenyl diisocyanate (MDI), which is polymerized with a diol (HO-R-OH) to give a polyurethane. Two moles of aniline react with formaldehyde to give />,//-methylenedianiline (MDA), which reacts with phosgene to give / ,//-methylene diphenyl diisocyanate. Toluene diisocyanate (TDI) also reacts with a diol to give a polyurethane, but polyurethanes derived from />,//-methylene diphenyl diisocyanate are more rigid than those from toluene diisocyanate. 

One way of obtaining the more useful cross-linked polyurethanes is by using a trifunctional reagent. Thus either the toluene diisocyanate can react with a triol or the propylene oxide can be polymerized in the presence of a triol. 

Toluene diisocyanate (TDI) is polymerized with diols to produce polyurethanes, which are used to make flexible foam for furniture cushions, mattresses, and carpet pads. 

This polymeric diol is then reacted with a diisocyanate, such as toluene diisocyanate, to produce the polyurethane ... 

Figure 4.8 Interfacial polymerization, using polyethyleneimine (PEI) crosslinked with toluene diisocyanate (TDI) to from the NS-100 membrane as patented by Cadotte (U.S. Patent 4039440, August 2,1977).

A polyurethane results when a diol reacts with a diisocyanate, a compound with two isocyanate groups. The compound shown next, commonly called toluene diisocyanate, is frequently used for making polyurethanes. When ethylene glycol or another diol is added to toluene diisocyanate, a rapid condensation gives the polyurethane. Low-boiling liquids such as butane are often added to the reaction mixture. Heat evolved by the polymerization vaporizes the volatile liquid, producing bubbles that convert the viscous polymer to a frothy mass of polyurethane foam. 

The polyisocyanates which can be used for preparing isocyanate-based foams are mainly aromatic compounds and some aliphatic or aralkyl polyisocyanates. TDI (toluene diisocyanate) is widely used for flexible foams. Pure MDI (diphenylmethane diisocyanate) is used for elastomers and coatings. Modified TDI and modified MDI are used for high-resilience flexible foams. Polymeric isocyanates (polymeric MDI or oligomeric MDI) are mostly used for preparing rigid urethane and isocyanurate foams, and in part, for preparing flexible and semi-flexible foams. 

Moreover, in situ polyurethane formation was performed by irradiation of the polymeric pyridinium salt in THF containing toluene diisocyanate and catalyst. It is clear that alkoxy pyridinium terminated polymers are useful materials as precursors for block copolymers and hydroxy functional telechelics. The latter are particularly attractive in photoinduced polycondensation and in applications where hydroxyl groups are needed to be protected. 

Polyurethane [117] and polyester [118] particles have also been prepared by the dispersion polyaddition of ethylene glycol (EG) and toluene diisocyanate (TDI) in paraffin, and the polycondensation of acid and ester at a high polymerization temperature, respectively. Table 3 provides an overview of microspheres of monomers other than vinyl monomers obtained by dispersion polymerization. 

Weyel, D.A., Rodney, B.S., Alarie, Y. (1982). Sensory irritation, pulmonary irritation and acute lethality of polymeric isocyanate and sensory irritation of 2,6-toluene diisocyanate. Toxicol. Appl. Pharmacol. 64 423-30. 

More recently, composite membranes have been made by interfacial polymerization or by in situ polymerization A representative case is illustrated in F. 8. Here, a microporous polysulfone membrane is used as a substrate. This membrane is soaked in a dilute aqueous solution of a low molecular weight polyethylenimine (PEI). Without drying, this membrane is then contacted with a crosslinking agent such as toluene diisocyanate (TDI) or isophthaloyl chloride dissolved in hexane, after which the membrane is cured in an oven. A highly crosslinked, salt-rejecting interfacial layer is formed in this way. A summary of the properties of three of the more important composite membranes is presented in Table 10. 

The one-shot methods used to produce flexible polyurethane foams employ quick mixing of a (usually) triol-based polyether of fairly high-molecular weight with toluene diisocyanate, catalyst, and water for gas production (Eq. 21.19). The reaction of water with the diisocyanate rapidly raises the average functionality in the polymerizing system by forming urea, as well as urethane links (Eq. 21.23). 

Adhesives which are meant to cure at temperatures of 120 or 171°C require curatives which are latent at room temperature, but react quickly at the cure temperatures. Dicyanodiamide [461-58-5], (TH INI is one such latent curative for epoxy resins. It is insoluble in the epoxy at room temperature but rapidly solubilizes at elevated temperatures. Other latent curatives for 171°C are complexes of imidazoles with transition metals, complexes of Lewis acids (eg, boron trifluoride and amines), and diaminodiphenylsulfone, which is also used as a curing agent in high performance composites. For materials which cure at lower temperatures (120°C), these curing agents can be made more soluble by alkylation of dicyanodiamide. Other materials providing latency at room temperature but rapid cure at 120°C are the blocked isocyanates, such as the reaction products of toluene diisocyanate and amines. At 120°C the blocked isocyanate decomposes to regenerate the isocyanate and liberate an amine which can initiate polymerization of the epoxy resin. Materials such as Monuron can also be used to accelerate the cure of dicyanodiamide so that it takes place at 120°C. 

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