Methylene diphenyldiisocyanate

The laser flash photolysis of aromatic diisocyanate based polyurethanes in solution provides evidence for a dual mechanism for photodegradation. One of the processes, an N-C bond cleavage, is common to both TDI (toluene diisocyanate) and MDI (methylene 4,4 -diphenyldiisocyanate) based polyurethanes. The second process, exclusive to MDI based polyurethanes, involves formation of a substituted diphenylmethyl radical. The diphenylmethyl radical, which readily reacts with oxygen, is generated either by direct excitation (248 nm) or indirectly by reaction with a tert-butoxy radical produced upon excitation of tert-butyl peroxide at 351 nm. 

Materials. Methylene 4,4 -diphenyldiisocyanate (MDI, Mobay) was recrystallized from cyclohexane. Toluenediisocyanate (TDI— represents mixture of 2,4- and 2,6-isomers in 80/20 ratio), p-toluidine (Aldrich) and aniline (Aldrich) were purified by vacuum distillation before use. Diphenylmethane, tert-butyl peroxide (TBP), 4-bromoaniline, butyl lithium in hexane, and ethyl chloroformate, were obtained from Aldrich and used as received. Spectrograde tetrahydrofuran (THF) and benzene from Burdick and Jackson were used as received. Poly(tetramethylene ether glycol) with MW 1000 was obtained from polysciences and dehydrated under a rough vacuum at 50 °C for 24 h. 

On the other hand, the photodegradation of segmented polyurethanes based on methylene 4,4 -diphenyldiisocyanate (MDI) is dependent on the physical structure of the polymer. Such segmented polyurethanes are formed from poly(ethylene oxide) (PEO) or poly(tetramethylene oxide) (PTMO) with various polyether polyols, which are chain extended with 1,4-butanediol (EDO) [680-682, 1006, 1321]. 

The most important commercial process is the reaction of MDA with an excess of phosgene to form the corresponding isocyanate, 4,4 -methylene-diphenyldiisocyanate, MDI, C H qN202- The reaction proceeds through the formation of a primary carbamyl chloride that is decomposed with heating and the removal of HQ. 

Hagmar L, Stromberg U, Welinder H, et al. 1993. Incidence of cancer and exposure to toluene diisocyanate and methylene diphenyldiisocyanate a cohort based case-referent study in the polyurethane foam manufacturing industry. Br J Ind Med 50(11) 1003-1007. 

MDI = methylene bis-diphenyldiisocyanate. HMDl = hydrogenated MDI. PTMEG = polytetrametyl ethylene glycol. EDA = ethylene diamine. BD = butanediol carbonate is a proprietary carbonate diol. 

Epoxidized plant oils such as castor oil can also be converted into polyols and copolymerized with isocyanates such as toluenediisocyanate (TDI) or methylene-4,49-diphenyldiisocyanate (MDI) to obtain PUs. Meier et al. [56] reported that canola, corn, soybean, and sunflower oil-derived polyols yield PU resins of similar cross-linking densities (and, consequently, similar glass transition temperatures) and mechanical properties, despite differences in fatty acid distribution. 

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