Diphenylmethane diisocyanate determination

Polyurethane networks were prepared from polyoxypropylene (POP) triols(Union Carbide Niax Polyols) after removal of water by azeotropic distillation with benzene. For Niax LHT 240, the number-average molecular weight determined by VPO was 710 and the number-average functionality fn, calculated from Mjj and the content of OH groupSj determined by using excess phenyl isocyanate and titration of unreacted phenyl isocyanate with dibutylamine, was 2.78 the content of residual water was 0.02 wt.-%. For the Niax LG-56, 1 =2630, fn=2.78, and the content of H2O was 0.02wt.-%. The triols were reacted with recrystallized 4,4"-diphenylmethane diisocyanate in the presence of 0.002 wt.-% dibutyltin dilaurate under exclusion of moisture at 80 C for 7 days. The molar ratio r0H = [OH]/ [NCO] varied between 1.0 and 1.8. For dry samples, the stress-strain dependences were measured at 60 C in nitrogen atmosphere. The relaxation was sufficiently fast and no extrapolation to infinite time was necessary. 

Fig. 3.6 shows the results of viscosity determination for a linear temperature increase in a polyurethane based on poly (butadiene diol), diphenylmethane diisocyanate, and diamine. 

Weisfeld (44) compared the catalytic activity of various metal acetyl-acetonates by measuring the time required for a certain polyethylene adipate ester-diphenylmethane-diisocyanate mixture to reach a predetermined viscosity in the presence of the catalyst and also used the same technique for determining the catalytic order n defined by... 

A reliable method to determine the oligo-polyol reactivity is the study of the kinetics of the oligo-polyol s reaction with phenyl isocyanate, a model for the -NCO groups of toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) ... 

Schulz M. and Salthammer T. (1998) Sensitive determination of airborne diisocyanates by HPLC 4,4 -Diphenylmethane-diisocyanate (MDI), Fresenius J. Anal. Chem., 362, 289-293. 

MDI method For determination of 4,4 -diphenylmethane diisocyanate in the atmosphere, 5 litres of air should be drawn through 3 ml of 0-4n hydrochloric acid. After the addition of three drops of a 0-6% (w/v) sodium nitrite solution six drops of 10% (w/v) sulphamic acid should be added and the mixture transferred to a separating funnel containing 2 ml of 1 n sodium hydroxide solution and six drops of a suspension of 0-5 g of 2-hydroxy-3-naphthoic anilide (Brenthol AS) in 50 ml water. This mixture is then shaken and 1 ml of 6n sulphuric acid followed by 3 ml of chloroform are added. This is shaken and the chloroform layer separated off. The colour of this chloroform layer is then compared with standard colour solutions prepared by mixing a solution of cobaltous chloride (as above) with a solution of 32 g anhydrous ferric chloride, 25 ml concentrated hydrochloric acid (SG 20°C 1-18) and 975 ml water. The proportions of these two solutions equivalent to different levels of atmospheric diisocyanate are given in Table 11.3. 

To illustrate the advantages and possible pitfalls of in-line measurements by IR spectroscopy with a light-fiber-coupled ATR probe, a recently investigated polyurethane solution polymerization will be discussed shortly. The principle experimental setup is outlined in Figure 45, which also shows the ATR diamond probe head as enlarged insert. In this reaction vessel, the polymerization of 4,4 -diphenylmethane diisocyanate (MDl) and 1,4-butanediol (1,4-BDO) in a 50/50% (v/v) chloroform/diglyme solution was monitored at temperatures between 40 and 70 °C. The background of the variable-temperature measurements was the determination of the reaction kinetics and the calculation... 

The crosslinking of polyurethane resin composed of diisocyanate derived from 4,4 -diisocyanate diphenylmethane and a low-viscosity polyethertriol was also investigated under micro-wave conditions. The reactions were carried out without a catalyst and led to final networks with mechanical properties least equivalent to those prepared under conventional conditions. For example, the average elasticity modulus determined from uniaxial compression with samples (25 mm of height and 12.5 mm of diameter) was equal to 3120 MPa for curing under... 

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