Polyaspartic acid ester

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Polyaspartic acid esters , ( polyaspartates , polyaspartics ), often also called asparagine esters for short , is a name for a group of compounds that are used as reaction components in "Very High Solids" 2-component polyurethane paints. The advantage of these compounds is their low viscosity and rapid drying and reactivity.

Manufacture and chemical constitution

The polyaspartic acid esters are produced by adding a primary diamine H 2 N-R'-NH 2 to the double bond of two molecules of the fumaric acid or maleic acid diester. The general structure is:

They are more precisely bis-N, N'-substituted aspartic acid diesters. Many variations are possible with the substituents R (alkyl-) and R '(cycloalkylene-). Due to the steric hindrance caused by the ester groups and their -I effect , which reduces the electron density on the nitrogen atom, the amino groups are limited in their reactivity towards isocyanates , the hardener components in the polyurethane varnish. The reactivity can thus be adjusted via the size of the aliphatic radicals R. Even if the reaction products of aspartic acid esters and polyisocyanates are often referred to as polyurethanes, they are actually polyureas .

application

Polyaspartic acid esters are used in combination with polyisocyanates, especially in industrial coatings, including the coating of large vehicles, and in corrosion protection . Due to the low viscosities, the paints are formulated with very little solvent compared to standard systems and are therefore environmentally friendly, i.e. H. low VOC values. The aspartic acid esters close a gap between OH-functional components such as polyesters or acrylates and reactive components containing amino groups. While the former are comparatively slow to react to the isocyanates used, have high solvent contents and correspondingly long drying times in the paint formulations or are cured under temperature control, the latter react extremely quickly and can only be applied using special mixing head systems. Aspartic acid esters, on the other hand, have a balanced relationship between pot life and low emissions . Together with low-viscosity polyisocyanates, formulations with VOC values ​​of 250 g / l can be achieved. The products are available on the market as 90-100% liquids with a viscosity range from 100 to 1500 mPas under the name Desmophen NH (manufacturer Bayer MaterialScience AG).

When exposed to thermal stress, adducts of aspartic acid esters and diisocyanates react with ring closure and condensation to form polyhydantoins , high-temperature-resistant polymers. This behavior may have been avoided. a. used for the production of electrical insulating varnishes .

literature

  • Ulrich Meier-Westhues: Polyurethanes / lacquers, adhesives and sealants . Vincentz Network GmbH & Co. KG Verlag Hannover, 2nd edition, 2007, ISBN 3-86630-896-5