Precipitation is the easier part: if you add e.g. alcohol, which is not a solvent of the product, it will precipitate. The question is whether the prepolymer obtained in the first step is also soluble in DMSO? What is the meting point of the chain extender? If you are lucky it may melt in the prepolymer obtained in the first step. What is the temperature in the second reaction step?

Dear Mr. Banhegyi, first of all thanks for the reply. I keep the reaction temperature at 80°C during all the steps. I added the diisocyanate to the polyol solution in dry DMSO, and the prepolymer seems to be soluble. The melting point of the chain extender is 114°C, too high for the reaction temperature. Do you think that I should raise the temperature in the second step?

Hi,

You can dissolve your chain extender in DMSO separately and add this portion at once or drop wise to the reaction medium. To precipitate the solution first precipitate in water to remove DMSO and chain extender and then in alcohol for your polymer. Try using cold alcohol for better precipitation.

Dear all;

firstable, you should first check some relevent chemistry because I think there will be a reaction between the DMSO and the isocyanate groups. The second thing is that you should check first may be the chain extender is soluble at 80°C in the reactants or in the prepolymer. Regards

Dear all;

this attached file supports my previous answer. Regards

Dear all,

to Parimal: what you mean with "first precipitate in water to remove DMSO and chain extender and then in alcohol for your polymer"?

With regard to the reaction of isocyanates with DMSO: I enclose an article that use this solvent to carry out the reaction, so, I think it is not a problem; but the solubility proof could be a good idea!

With regard to the reaction: in solution, I need catalyst to perform the reaction?

Is there a known solvent for your chain extender? If yes, does it mix with DMSO? Then you may utilize Parimal's idea to add the chain extender in a solvent. Regarding catalyst: if you chose to increase the temperature you may try without catalyst.

You can use one-step solution polymerisation method is easy method

The polyol based polyester  + chain extender warmed to 120C and spun.

The mixture then cooled and added the MDI and warmed again and stirred for 2 hours

And then coagulated into water for 2 minuets, the result a white fibrous PU that had properties of rubber

Dear all,

anyway I have gone rapidly through the attached file, I see that they did not payed too much on basic chemistry. Thermal and mechanical analysis do not really tell what is happening on the chemistry level or on the reaction kinetics. I suggest to use DMF instead of DMSO may be it works. Regards

Dear all;

in my previous answer I suggested the use of DMF instead of DMSO, however, after checking some literature, I found that the same problem for DMSO holds for DMF. I attached two files, one on the reaction of Isocyanates with DMF, and a second one an introduction on polyyrethane.

THE POINT I WANT TO STRESS ON IS THAT ONE SHOULD GIVE SOME CARE WHEN WORKING WITH REACTIVE SOLVANTS, SINCE THEY MAY INTERFERE WITH THE NORMAL COURSE OF A GIVEN CHEMICAL REACTIONS. Regards

I concur with the opinions with those given by Bouaziz that the use of DMSO and DMF should be careful because of their reactions with isocyanate at high temperature (150 C) and its hydroscopic nature. Actually, DMSO should be distill over CaH2 before use to eliminate its water or it will be difficult to make a high molecular wt. PU products. In our experiments, two solvents might be good for your trial; DMAc and TMS. They have high bp as well as polarity and less tendency for water absorption. After making the prepolymer in neat condition, then the hard segment diol solution of DMAc or TMS can be added into it. They can be vaccum removed after the reaction but not completely. For the best convenience, dilution of PU product in large excess of water will solidify your PU product. After vacuum oven drying of the product, PU can be obtained free from the solvent. Try it and it works for us.

Dear all,

thank you for the reply. I searched and I found that Mr. Abdelkader is right about the use of DMF and DMSO as solvent for the preparation of PU, because of their reaction with the iscocyanate leading to amine and sulfilimine derivatives respectively. However, I perform the synthesis in DMSO and the 13C-NMR show clearly the uretane formation; so probably the adverse reaction happen only at high temperatures as Mr. Shenghong suggested. I found some literature that use 1,4-dioxane (bp = 101, 1°C) as solvent for the reaction, that could be an ineresting alternative.

To Mr. Shenghong: the neat prepolymerization and the subsequent addition of solubilized chain extender is a good idea, I will try it. Thank you for the suggestion.

I still have a doubt: Is there any difference in precipitation with water or alcohol? If yes, which is the better one?

Fabio,

Dioxane should also work as a solvent. We used it for reactions between isocyanates and alcohols in this paper: DOI: 10.1002/pola.25887 We also used DMF (90 °C) as solvent for TPU polymerization. We did not see problems at 90C but maybe problems occur at higher temps. What ever solvent you use, make sure you dry it (and your starting monomers as well). Good luck.

SC Ligon

Hi everyone,

Is it possible to do this reaction in DMSO at last ? I did not understand the precipitation part. I want to try this reaction with polyol and isocyanate with little amount of catalyst. Which is the best solvent ?

It depends to molecular weight you want to approach and the time you want to spend. if you want to achieve polyurethane with high molecular weight you can use 3 step bulk polymerization. in this method desired amount of polyol and disocyanate in reactor vessel and directly before addition of catalyst or chain extender mix them together by increasing molecular weight you should increase the temperature in three step to always have liquid poly urethane which in the last step by reviving to calculated molecular weight it remains liquid in certain temperature so you can add chain extender increase the temperature a bit cast it in desired molds. but don't remember in this method you should have enough information about melting point of your target polymer and its molecular weight , which make it easy to play wit temperature, second always use antioxidant and try to do this method in nitrogen atmosphere it is easy to reach high and ultra high molecular weight polyurethanes and ultra high molecular weight.

the second method is solution polymerization use at least 25% toluene to control viscosity the main problem of this method is the low molecular weight of obtained polyurethane