One of our first major projects in the Aminovation Lab™ is nearly complete!
We started a project several months ago investigating two different methods to convert the fast reacting primary amine groups in Dytek® A to slower reacting secondary amines. Our study looked at these derivatives in an isocyanate system and compared their performance to similar commercially available curatives.
The first route reacts Dytek® A with isobutyraldehyde to make the aldimine derivative. The other route utilizes the Michael Addition reaction of a conjugated nitrile (in this case Dytek® 2PN [2-pentenenitrile]) reacted with a primary amine. The Dytek® A component is highlighted in blue.
Aldimine Chemistry
Because there are no active N-H groups, aldimines cure very slowly when mixed with an epoxy resin or with an isocyanate. They function as a latent curing agent by essentially blocking the free primary amine until exposed to moisture in the air.
Existence of a possible tautomer with active N-H groups could provide some reactivity prior to hydrolysis, but the generally accepted belief attributes the predominant curing mechanism to the free amine.
Almost any primary diamine can be used as a starting material, but a common commercially available product uses isophorone diamine (IPDA) and isobutyraldehyde. Our recent study compared this curative to one made from Dytek® A and isobutyraldehyde in an isocyanate containing system. What we found was that compared to the IPDA aldimine, the Dytek® A aldimine exhibited:
- Equivalent Shore D hardness
- 6x higher maximum tensile stress at break/yield and 2x higher tensile modulus
- 3x greater elongation
- Less brittleness
- Similar chemical and water resistance
- Higher onset temperature for thermal degradation (237.8°C), vs. (111.5°C)
- Better aged mechanical properties
Please contact us to learn more about this Aminovation Lab™ project at Dytek@INVISTA.com. We have samples available. This molecule is also already TSCA registered.
Another idea we have using this chemistry exploits the differential reactivity feature of Dytek® A. Since the unhindered amine end in Dytek® A has a reactivity 2.5x faster than the more hindered end, we think we could selectively react one end with isobutyraldehyde creating a curative that can react fast and then give a second cure after hydrolysis.
Look for the results of the Michael Addition chemistry curative in the next CASE Study article.