[mufan]

hello guys,
This one might be a little tough.  I am working with Polyurethane dispersions (PUD), which is basically polyurethane prepolymers suspended in water with the help of a surfactant. 

I want to increase the dry time of the PUD by reacting out the water rather than waiting for it to evaporate.  Evaporation is impeded because the top of the PUD skins over and acts as a blanket which traps the water inside preventing it from evaporating.

I know that putting an isocyanate in the mixture will react with the water to form a polyurea.  This would be perfect because it reacts slowly (not exothermic) and it reacts out the water.  The problem is that isocyanate is very nasty. 

So do any of you organic gurus know of a no exotherm or low exotherm reaction with water that would take place at ambient conditions to slowly form a solid material or polymer that doesn't involve something really nasty?

[Custos]

Define "nasty".  Seriously, if something reacts with water it will be nasty to biological systems pretty much by definition. Your isocyanate idea is as good as any - perhaps you could tune the reactivity by using a hindered isocyanate.

[mufan]

Isocyanate is a real no no.  Not so much an inhalation hazard but a bad irritant and desensitizer.  The problem with it is that it sticks around for a long time and you can be exposed to it months afterwards.  It is not an option for the work I'm doing. 

Any other polymers that form in the presence of water?