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:
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>-, 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,
Hope this helps a bit... Good Luck!
R. David Zopf
Bomar Specialties Co
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.
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
R. David Zopf
Bomar Specialties Co.
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?
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.
You could use an articifical thixotrope such as fumed silica (Cab-o-sil)
rather than relying on the short chain amine.
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