Polyurea

Polyureas are polymers resulting from the polyaddition of isocyanates and amines. The polymer has a structural element that is similar to the urea: - [ -NH -R -NH-( C = O) -NH -R' -NH-( C = O) -] n- structure, they belong to the amino.

Production

The isocyanates used may be a monomer ( having at least 2 isocyanate groups ), so-called prepolymers or polymer will be used which are prepared from polyols with an excess of isocyanate, and therefore contain isocyanate end groups.

The amines required can be added as a second component or can be generated from the isocyanates by reaction with water.

Again, you have two options:

  • The water is used as the second component is added ( two-component systems, usually in combination with polyols ) - this is a common method for the production of polyurethane foams
  • Curing takes place with water vapor from the air ( one-component )

In both methods produced carbon dioxide, which brings the polymer foaming. But can be quite homogeneous with single-component, non-foamed coatings can be prepared when the layers are thin enough and so the carbon dioxide can diffuse fast enough from the polymer layer. This is utilized in single-component polyurethane coatings. If you want to achieve thicker layers, the CO2 can be attached to, for example with the aid of calcium oxide. A further possibility of producing non-foaming one-component coatings, is to combine the so-called latent curing agents with isocyanates. This can be, for example, oxazolidines hydrolyze with water to form amino alcohols, which then react with the isocyanate groups to urea and urethane groups.

Properties

Two-component systems of aliphatic amines and isocyanates react due to the high nucleophilicity of the amines usually very quickly and need to be processed by machine with two-component mixing plants - the pot lives are in the range of seconds. But there are also much less reactive, mostly aromatic amines available that allow processing by hand. These include, for example, 4,4 '-methylene- bis (2- chloroaniline) ( MBOCA ), bis Methylthiotoluylendiamin, N, N'-bis (sec - butylamino ) diphenylmethane and diethyltoluylenediamine. In addition, aliphatic amines are available, such as polyaspartic esters, which also react relatively slowly, but in contrast to the non- aromatic amines tend to discolor. Polyureas exhibit good to very good chemical resistance and high elasticity and tensile strength.

Use

  • Coatings
  • Elastomers
  • Adhesives
  • Coatings
  • OCF
  • Situ
  • Foams

Swell

  • Kittel, Textbook of paints and coatings, 2nd Edition, Volume 2: Binder for solvent-borne and solvent-free systems, ed Walter Krauss, S. Hirzel Verlag 1998, ISBN 3-7776-0886-6.
  • Rompp CD 2006, Georg Thieme Verlag 2006
Addition polymer Hydrolysis
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