polyurethane/urea elastomers

When making a 2k polyurethane/urea elastomer what can you use as a
compatibiliser to stop the amine and ether polyol components phase
separating as they react with the diisocyanate at different rates?
Thanks
Colin
Reply to
Colin Reed
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You're trying to one-pot a PUU? From what I've heard/seen, a more typical method is to make a prepol out of your polyol-iso before adding the amine to chain extend. Differential reactivity is rendered irrelevant if you run reactions one after the other ;-)
Section 3.2 of this thesis:
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describes a good lab prep method for PUU's. I've only seen a PUU made in an extruder once, but they were running a prepol before extrusion, too, then putting the prepol in the axial, and introducing their amine via sidestream. That gave a big differential in volumes introduced. They had a twin screw with L>=2D, and the pumps were running flat out (high flow rate in the constriction). I don't know if that setup is typical of production scale, or not...
Hope this helps a bit... Good Luck!
Regards, R. David Zopf Bomar Specialties Co
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Reply to
David Zopf
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Thanks. I'll have a read of that. The main problem is that this is to be applied from a cartridge system and so it has to be in two components with a 1:1 mix ratio. The prepolymer is a polyether urethane prepol but the second component needs to be a mix of amine and polyether just to get the required reaction time and physical properties. I've seen reference to mixing amine and ether in this way but at the moment I just get a grainy mix as the amine components react quicker than the ether, and then a very "cheesy" state when I start to get phase separation. I just wondered if there was some way of improving compatibility so they didn't separate quite so much during the reaction stage. I've also seen reference to people using castor oil in the prepolymer rather than a polyether. I wondered if this was just a cost thing, or whether the castor oil or any ricinoleic acid ester helps with compatibility in some way.
Cheers
Colin
Reply to
Colin Reed
Ug. Better you than me ;-) This is why I went the route of radcure urethane acrylates... One pack, sane Mws, chain growth polymerization doesn't rely on stoichiometry, room temperature cure, etc, etc. Does the app. really need to be a 2K PUU? I could track down a good UV FIP gasket formulation for you...
What's your choice of polyether? PTMEG would be my first guess as a good choice, but maybe you need to do a solubility screening of a couple different polyols at different Mws with your amine. I seem to recall BYK Chemie having some PUU stabilizer additives, too. You might want to check out their website.
Unsaturation interacting favorably with the amine nitrogen lone pair? If its significant enough, they should admix well, even in the abscence of an isocyanate.
Regards, R. David Zopf Bomar Specialties Co.
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Reply to
David Zopf
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Colin,
We used to get this problem when formulating spray elastomers with short-chain amines for thixotropy.
The only possible way we found to get rid of the problem (which is phase separation) is to use a higher mol weight amine, but then you don't get the thixotropy. Maybe this isn't a problem for you?
Rgds,
Simon
Reply to
Simon Kay
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>>
Hmm. Unfortunately I need the thixotropy for the application. I can get it by dumping the polyol and replacing with a plasticiser but then the reaction is way too fast for the application. I can see that this one is going to take some time.
Colin
Reply to
Colin Reed
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You could use an articifical thixotrope such as fumed silica (Cab-o-sil) rather than relying on the short chain amine.
Rgds,
Simon
Reply to
Simon Kay

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