Polymeric MDI

The isocyanates used with rigid foam systems are either polymeric MDI or specialty types of TDI. Both contain various levels of polymerized isocyanate groups which contribute to molecular weight per cross-link and also may affect reactivity due to steric hindrance of some isocyanate positions. 

Commercially, polymeric MDI is trimerized duting the manufacture of rigid foam to provide improved thermal stabiUty and flammabiUty performance. Numerous catalysts are known to promote the reaction. Tertiary amines and alkaU salts of carboxyUc acids are among the most effective. The common step ia all catalyzed trimerizations is the activatioa of the C=N double boad of the isocyanate group. The example (18) highlights the alkoxide assisted formation of the cycHc dimer and the importance of the subsequent iatermediates. Similar oligomerization steps have beea described previously for other catalysts (61). 

Other approaches have explored the reaction of amines with dimethyl carbonate or its precursors (28). A reaction scheme for the production of polymeric MDI is as follows ... 

Commercially, the PMDA mixtures are normally treated with phosgene to produce the corresponding isocyanates. These isocyanate mixtures, commonly called polymeric MDI (PMDI), are sold direcdy and have varied chemical compositions. The 4,4 -MDI can be separated from the PMDI products by distillation or crystallisation (31,32). The amount of 4,4 -MDI that is removed depends on marketing conditions. The residues are also viable commercial products. 

Polymeric MDIs, which are also used in polyurethane foams, usually have a lower reactivity than the monomeric material but are also less volatile. The polyisocyanurate produced from this material will be of the type shown in Figure 27.11. 

When this is carried out in suitable solvents at temperatures in the range 75-120°C, soluble products will be obtained. Polymeric MDI is usually used as the isocyanate component and this results in a stiff chain molecule. One such product is reported to have a of 200-220°C. 

The most commonly used isocyanate in urethane adhesives is MDI. The pure material methylene diphenyl-isocyanate is a solid that melts around 37°C. Many variations of MDI are commercially available, and these variations fall into three major classes monomeric MDI, modified MDI s, and polymeric MDI s. 

Polymeric MDI s Low-intermediate 2.1-2.5 Brown liquid Semiflexible, 2-K foam adhesive... 

Several large applications for one-component moisture-cure urethane adhesives are available. Polymeric MDI is an exceptional binder for wood products, such as oriented strand board and particleboard. One-component urethane windshield adhesives are used almost exclusively in both the OEM and automotive aftermarket. One-part urethane adhesives are used to assemble the sidewalls for recreational vehicles (RV s), manufactured housing, and mobile homes. In construction applications, one-part urethanes are used to bond metal doors, hardwood flooring, panels, and partitions. 

A variety of applications exist for liquid, 100% solid adhesives, (An adhesive is considered 100% solid if there is no solvent in the adhesive.) Some of the largest uses include structural wood adhesives and adhesives used for the transportation industry, such as windshield adhesives and those used for bonding composite sidewalls of a recreational vehicle (RV). Structural wood adhesives are often made of a polymeric MDI with functionality of approximately 2.7 or higher. Rigid assemblies often utilize polymeric MDI, whereas flexible adhesive assemblies will more often utilize pure MDI, a solid waxy material that melts at around 37°C, or a modified MDI , i.e., MDI that has been modified to make it a liquid at room temperature. Prepolymers are made with ratios of anywhere from NCO/OH = 1.6 to 3.0 or higher. 

Liquid polyester MDI prepolymer, 9% NCO Liquid polymeric MDI, 2.2 functionality Polyol component ... 

Polylactides, 18 Poly lactones, 18, 43 Poly(L-lactic acid) (PLLA), 22, 41, 42 preparation of, 99-100 Polymer age, 1 Polymer architecture, 6-9 Polymer chains, nonmesogenic units in, 52 Polymer Chemistry (Stevens), 5 Polymeric chiral catalysts, 473-474 Polymeric materials, history of, 1-2 Polymeric MDI (PMDI), 201, 210, 238 Polymerizations. See also Copolymerization Depolymerization Polyesterification Polymers Prepolymerization Repolymerization Ring-opening polymerization Solid-state polymerization Solution polymerization Solvent-free polymerization Step-grown polymerization processes Vapor-phase deposition polymerization acid chloride, 155-157 ADMET, 4, 10, 431-461 anionic, 149, 174, 177-178 batch, 167 bulk, 166, 331 chain-growth, 4 continuous, 167, 548 coupling, 467 Friedel-Crafts, 332-334 Hoechst, 548 hydrolytic, 150-153 influence of water content on, 151-152, 154... 

Polyurethanes Expo 99. Conference proceedings. Orlando, FI., 12th-15th Sept. 1999, p.455-9 REPORTING EMISSIONS TO EPA S TOXIC RELEASE INVENTORY HOW SPI POLYURETHANE DIVISION S COMPLIANCE ASSISTANCE TOOLS HELP MDI AND POLYMERIC MDI REPORTERS DO ABETTER JOB... 

The lARC has determined that there is inadequate evidence for the carcinogenicity of MDI or polymeric MDI in humans and that... 

Reuzel PGJ, Arts JHE, Lomax LG, et al Chronic inhalation toxicity and carcinogenicity studies of respirable polymeric methylene diphenyl diisocyanate (polymeric MDI) aerosol in rats. Fundam Appl Toxicol 22 195-210, 1994... 

MDI offers a number of advantages. First, it is somewhat safe to use based on its much lower vapor pressure and is available in convenient forms. It is produced by the reaction of an amine and phosgene. The result is a mixture of multi-ring isocyanates. The purest form is the two-ring isomer shown in Figure 2.2. The isomer is recovered by distillation. What is left behind is the so-called polymeric MDI that... 

It is important to be aware of the chemical effects of isocyanates. The polynre-thanes you will develop will be combinations of polyols and isocyanates. The ratio of the two compounds will in pait dictate both the physical and chemical properties of the product. As a general rule, the isocyanates are hard segments that impart rigidity to the polymer. The polyol is the so-called soft segment. The various molecular weights (more correctly equivalent weights available in the form of polymeric MDIs) provide certain advantages. Table 2.2 lists a few commercially available polyisocyanates and their physical properties. 

Synonyms Bis(l,4-isocyanatophenyl)methane diphenylmethane diisocyanate MDI methylenedi-/ ara-phenylene isocyanate and for 26447-40-5 crude MDI polymeric MDI PMDI generic MDI non-isomeric-specific MDI... 

Reuzel, P.G.J., Arts, J.H.E., Lomax, L.G, Kuijpers, M.H.K., Kuper. C.F., Gembardt, C., Feron, V.J. Loser, E. (1994) Chronic inhalation toxicity and carcinogenicity study of respirable polymeric methylene diphenyl diisocyanate (polymeric MDI) aerosol in rats. Fundam. appl. Toxicol., 22, 195-210... 

Polymeric MDI -flexible foam from [FOAMED PLASTICS] (Vol 11)... 

Since I -) [. the overall demand for isocyanates lias increased ul a compounded rate ul 12%. Although this level will nut likely he sustained in the future due to the maturation of key application markets, it is pruhablc hat additional growth will occur through the year 20011. This trend will likely include a shift in emphasis from TDI to MDI and polymeric MDI-hased materials. New growth opportunities in the construction industry, structural applications, and growth in the automotive industry exist. Third-world markets are also anticipated to provide growth opportunities. 

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. 

A rigid, foamed crosslinked PUR, usually with closed cells, is formed by the reaction of a diisocyanate and often methane diisocyanate (MDI) or polymeric MDI with polyester or more usually with a polyether polyol. Foaming may result from the water, which reacts with isocyanate groups to form carbon dioxide but is usually the result of using other... 

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