The problem of dehydration in polyurethane prepolymers
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Using toluene as a solvent and dehydrating it together with PEG (of course, almost half of the toluene will also be distilled off) – will this achieve the dehydration effect? I saw that some foreign studies used this approach; since the boiling points of toluene and water are similar, I have doubts about this method. Thank you all for your answers!
Can this method remove water from both toluene and PEG at the same time?
Agree with the 2nd floor. The laboratory method is feasible, as long as the dehydration is carried out to a certain level! ! !
Option 2: Use molecular sieves, but the molecular sieves need to be pre-treated. I’m not sure whether a regular flask can be heated to 200°C under vacuum Going back upstairs, vacuuming it out probably isn’t a good idea; after all, toluene is pumped into those tubes, and over time the tubes will dissolve… This post was last edited by tingyi on 2008-11-17 at 13:17
I agree with what was said on the 2nd floor; it is feasible to add toluene to the laboratory and use heating to remove water
If the vacuum level is sufficient, simply heat the PEG to 120 degrees, stir while applying vacuum, and proceed for 1–2 hours
Azeotropic water removal is possible. But, OP, are you saying you want to remove water from the prepolymer or only the PEG? . . What peg are you using? In PU synthesis, except for water used for foaming, all other waters are strictly prohibited. If the water content is low, molecular sieves are a great choice. If there is still excess water, vacuum dehydration is better. Molecular sieve 4A, yeah.
It’s about removing the water from PEG and the solvent toluene. There isn’t much water in PEG 6000; molecular sieves are available, of types 3A and 4A. I plan to use these molecular sieves to remove the water from toluene, and then apply vacuum to PEG. It’s a more conservative approach… haha, it’s just quite troublesome. I’ll try a method for direct dehydration next time. Thank you to everyone who commented above! If you have any good ideas, please share them plenty!
That shouldn’t be very troublesome. Are you using NCO-terminated ones? Your method is the common one; that’s exactly how I do it. However, I suggest dividing the medication into separate portions! PEG and isocyanate. After processing, package separately. . . Otherwise, it won’t work after opening the lid a few times. . . Hehe, I’ve already suffered losses. . .