Polycarbodiimides

Properties and Applications

Polycarbodiimides (CDIs) are highly reactive functional resin modifiers having excellent compatibility with a wide range of resins. They can be prepared by treating sterically hindered mono- or polyisocyanates with basic catalysts with simultaneous elimination of carbon dioxide.^1,2

Carbodiimides react with a variety of functional groups including alcohols, thiols, amines, and carboxylic acids. However, the reaction with alcohols proceeds too slowly (days-months) and with amines too fast (seconds) to be useful for most practical applications, whereas CDIs react in minutes to hours with carboxylic acids yielding N-acylurea compounds, and thus can be used as crosslinkers for polymers containing carboxylic acid groups.

Polycarbodiimides are mainly used as modifiers and cross-linking agents in solventborne and waterborne products such as paints, coatings, adhesives and inks. They allow for ambient or low temperature drying and cure, higher solid content and when used in coatings, they improve wear, abrasion and chemical resistance. CDIs are also extremely easy to use and have a much longer useful pot life than isocyanates.³
Recently, stable water-based CDIs have become available as well that possess a long pot-life when used as crosslinkers in aqueous acrylic or urethane latices containing carboxylic acid groups. Other advantages of these new developments include low/zero VOC and low/no toxicity.³

Manufacturers & Distributors

¹US Patnet 5,498,747; S. Pohl et al.; Carbodiimides and/or oligomeric polycarbodiimides based on 1,3-bis(1-methyl-1-isocyanatoethyl)benzene (1996)

²US Patent 2006/0194939; U. Licht & K. Haberle; Aqueous dispersions consisting of polycarbodiimides (2006)

³A. J. Derksen, PCI Journal, May 2017 & Asian PU Digest, vol. 2, no. 1, pp 36-41, 2018