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Study of the catalytic selectivity of an aqueous two-component polyurethane system by ftir spectroscopy

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Author(s): Stamenković Jakov V. | Cakić Suzana M. | Nikolić Goran S.

Journal: Hemijska Industrija
ISSN 0367-598X

Volume: 57;
Issue: 11;
Start page: 559;
Date: 2003;
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Keywords: Coatings | Waterborne polyurethane | Metal catalyst | IR spectroscopy

ABSTRACT
The difficulty in formulating a two component waterborne polyurethane, is the isocyanate-water side reaction, which can lead to gassing/foaming, loss of isocyanate functionality, low gloss and a reduced pot life. To compensate for this side reaction, these formulations usually contain a large excess of isocyanate. Tin compounds, especially dibutyltin dilaurate, are widely used in coatings as catalysts for the isocyanate/hydroxyl reaction. Because of the high aquatic toxicity of some organotin compounds, there has been an attempt to ban organotin compounds from all coating applications. As a general rule, organotin catalysts are not selective, they catalyze the reaction of isocyanates with both hydroxyl groups and water and also catalyze the hydrolysis of ester groups. One novel approach to control the water side reaction is the use of catalysts which selectively catalyze the isocyanate-polyol reaction and not the isocyanate-water reaction. The selectivity of a variety of metal catalysts (metal octoates, metal acetylacetonates and mangan chelates with mixed ligands) to catalyze the preferred reaction was measured using the FTIR method.
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