I was synthesized polyurethane and characterize using DSC. I was found 2 peak of Tm, the first is in 340 C and the second was in 430. Does my polymer forming some compound after decomposed thus it has 2 melting point? or what really happend to it? Thanks
DSC working properly? Are You sure polimerization of PUR was ended fully?
The temperatures you mention seem clearly too high to be ascribed to the melting point of thermoplastic polyurethane, as it can be generally expected to occur within about 120 ― 240 ºC. You are possibly dealing with thermosetting polyurethane.
Dear Ozi
It seems that in your compound there are portions that after first melting and breaking, new reactions between reactive sites was occurred which lead to another melting point. Your products can probably be as insulating polymers for heat and fire .
There are couple of possibilities, some of them are already mentioned above
- Partial degradation of polyurethane
- Two distinctly different polyols or isocyantes were used to synthesize your polyurethane, in that case heterogenic polyurethane can give two melting point
- Unreacted portion that gets reacted at higher temperature (very unlikely as the temperature you mentioned is too high).
Look at a study of one of our RG members:
https://www.researchgate.net/publication/239098416_Characterization_of_polyurethane_resins_by_FTIR_TGA_and_XRD
You' will see from the TGA that generally above 300ºC degradation occurs. So I do not see the point than to use DSC for characterization? What do you expect to see at such high T's?
For typical urethane Tg's you can find a collection in J. Brandrup, Polymer Handbook, 2nd edition page III-163-164. (for the 3rd edition I do not know the page numbers). Remember that a Tg (which....!!!) is a/o dependent not only upon the choice of the monomers but also on the MW..... So the given Tg's you'll have to check the primary literature given in order to understand the Tg in Brandrups table...
You will see that typical Tg's, even from hard PUR's, are not in the area were you run your DCS now, more a region to run a TGA study.
Article Characterization of polyurethane resins by FTIR, TGA, and XRD
Dear Ozi,
First of all look to your DSC traces and find where is exo and endo direction? This is the background to describe the transitions from DSC. Every kind of transition has his own view. Completely different trace is for Tg and Tm or degradation.
I have been working with characterization of PU with DSC for a very long time but I have never met Tm for PU higher than 220-240 Celsius. But we do not know the chemistry of your hard segments-may be you have special diisocyanates. Who knows?
Crosslinked PU rather do not crystallize - my comment for some answers.
Cystallization of PU strongly depends on chemistry, technology and DSC parameters of the analysis. And this is rather weak transition, very often you even need bigger samples to notice it in DSC. It is not like PE or PP behaviour.
Moreover it is very important to check delta H- is it realy very clear tarnsition or rather some weak changes in DSC run.
Read my papers- you can find some information on crystallization of PU.
And do run for a known substance, with a particular Tm - then you will see where is going peak from Tm.- if you do not have the experince with DSC description.
Good luck
Helena Janik
Gdansk University of Technology
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