Can a non-thermoplastic polyurethane be dissolved in an organic solvent, like THF?
By non-thermoplastic, I refer to a polyurethane made with a tri-functional polyol
The answer is definitely no, unless you are below the gel point. if you have a real network, it will only swell but will not dissolve. The fact is that many polyurethanes (even those with supposedly only linear strcture) may exhibit gl fraction due to branching or slight network formation (vlucanization). This is due to the fact that even urethane groups may react further with isocyanates (although at a slower speed) and most polymeric isocyanates have an average funcitonality ABOVE 2,00.
another question.... using the two-step process... a professor told me that when you have mixed and reacted the three components (Isoc + Pol + Ch Ext) you will obtain a rigid solid... But in the related papers they say that you will obtain a viscous liquid, and after the curing treatment you will get the solid PU...
So... what about it?, who is right?
It depends on a series of factors: on the molecular weight of the soft segment, on its rigidity, on the ratio of the soft to hard segnet, on the type of the ioscyanate etc. It is advisable t condcut the reaction so in two step reactions that the prepolymer obtained in the first step is still liquid, otherwise it will not easily react with the chain extender.
If the reaction surpassed of gelation point, the resulting polyurethane will be swelled. But the solubility will be approximately impossible.
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