I am a postdoctoral Research Scholar from National Institute of Material Advances (NIMA), Pittsburg State University, USA. Currently I am trying to synthesis a Polyurethane acrylate oligomer from vegetable oil precursor, I am quite obvious that my desired product was formed (FT-IR analysis) but main problem is gel formation during reaction even after the use of methyl ethyl ketone as solvent.
Please suggest me how could I avoid the gel formation for my reaction purpose because I want to get the polyurethane oligomer in viscus liquid form?
Chandan Bodhak Could you describe your reaction more in details, please?
Does your prepolymer contain free NCO or OH groups?
What do you use as a polyol in your reaction and what is the average functionality of this component? The greater functionality, the greater excess of NCO you would need.
I would recommend measuring water content of your polyol. Water could lead to unwanted side reactions.
What type of isocyanate do you use? Di- or poly-? Aliphatic or aromatic?
Aromatic di- and poly- isocyanates give very viscous prepolymers and reaction rate is high as well. At high concentration and elevated temperatures there is high risk of trimerisation and gel formation. I have faced similar problem. What temperatures do you use and how do you add your isocyanate? How do you control the reaction process?
As Oleg Novikov suggested it is highly recommended to terminate a reaction with adding, for example monofunctional alcohol, if we are speaking about oligomer without free NCO groups.
And test your MEK on peroxide content as you are working with vegetable oils. I have experienced gel formation using pretty old solvents. There is high probability of extra linkage formation whan system contains double bond from vegetable oil
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