Polyethylene glycol, reaction + diisocyanates

Polyurethanes (PU s). SL and 4,4 -diphenylmethane diisocyanate (MDI) were dissolved in tetrahydrofuran (THF), and the solution was stirred for 1 hr at 60°C. A THF solution of polyethylene glycol (PEG 400) and diethyl bis(2-hydroxyethyl)aminomethylphosphonate (polyol containing phosphorous) was added to the reaction mixture, and the reaction time was extended for 1 hr. In all reactions, the molar ratio of the total amount of isocyanate groups to the total amount of hydroxyl groups (NCO/OH) was maintained at 1.2. The lignin content in PU was 20 wt%. Each solution was drawn on a glass plate, and allowed to dry for 48 hr. The residual solvent in a sample was removed under vacuum and curing of each PU film was carried out at 120°C for 3 hr under a pressure of 50 kg/cm2. 

In the next experiment, a 1.05 molar excess of isopherone diisocyanate (IPDI) was dissolved in polyethylene glycol (ca. 6000 MW, hydroxyl = 3, nominal) and heated to 125 C under nitrogen. The viscosity at 25°C and the residual NCO (shorthand for isocyanate) content were detemuned. Figure 2.7 shows the increase in viscosity over tune. The NCO concentration, a measure of the extent of the reaction, was determined by a method discussed in the next chapter. 

The diisocyanates are used mainly in the manufacture of polyurethanes (PUR). These are produced by polyaddition of diisocyanates and dihydric alcohols, in particular the polyether alcohols (i.e., polyethylene glycols, polypropylene glycols, and the reaction products of propylene oxide with polyhydric alcohols). In addition, oligomeric esters from dicarboxylic acids and diols (polyester alcohols) are also used [91] ... 

Note that the terminal groups on the polymers prepared in reactions 1 and 2 are free hydroxyls. Thus, if a diisocyanate is reacted with a mixture of these two polymers the adipic acid-propylene glycol ester polymer may be linked to the polyethylene glycol. The final polymer contains blocks of ester and polyglycol joined by a urethane linkage and is known as a block polymer. It is interesting to note that only a small amount of isocyanate is required since the number of free hydroxyls is very few. 

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