To make polyurethane, TPU pellets are melted with DMF or THF solvent.
Q1. Is the urethane bond between diol and isocyante broken by the solvent?
Q2. When the solvent is volatilized, a urethane bond is formed between the diol and isocyanate again?
Chemistry expert, please give me an answer.
In common solubilization case urethane bond remains intact.
Solvent interacts with a whole chain and "weakens" intramolecular bonds between different TPU chains. Therefore their mobility increase and system is converted into liquid state.
When you remove a solvent intramolecular connections become strong again. Chain mobility becomes lower and system turns solid.
Igors Sivacovs
Thanks for your answer.
To summarize, the organic solvents liquefy TPU by weakening the non-covalent bonds between TPUs, right?
Dear all, in some situations yes, the urethane linkage is prone to hydrolytic scission. It is possible that the solvents are not dry enough. There are many factors influencing such hydrolytic chain degradation reaction. My regards
https://doi.org/10.1021/ma500904d
Abdelkader BOUAZIZ Thank you for answer. You mean that when polyurethane is added to a solvent in which a few water molecules remain, very slight hydrolysis may occur, right?
Abdelkader BOUAZIZ I think hydrolytic scission is a little bit out of scope of what Sangyub asked. In an article you shared, there is a solid polymer immerged in buffer solution over a period of 1 year.
Sangyub asked if urethane bond is breaking down into diol and isocyanate and formed again when TPU pellets are melted with DMF or THF solvent.
Feel free to correct me, but as far as I know, it does not happen. Some degradation possible via hydrolytic scission you mentioned, but as unwanted and irreversible side reaction.
Sangyub Oh yes. That's right. And in some degradation of main chain is possible, as Abdelkader mentioned.
My answer gives only a possible suspected reason. Urethane group breaking is well explored in polyurethanes self-healing polymers. The paper I attached is just a sample chosen arbitrary, but the author of the question can search for more specified one, if he find it interesting.
The urethane bond is not broken by most solvents, however in the molten state oxidation or degradation of the PU in solvent is possible;
the overall molecular interactions in the molten state are weaker.
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