Structural engineering of polyurethane coatings for high performance applications

This review addresses trends in the development of high performance polyurethane (PU) and its subclass coatings. Changes in the understanding the technical requirements and properties, along with novel approaches in creating high performance PU films are discussed. Some discussion of developments leading to the current status is provided, along with opportunities for the development of architectural, domestic and automotive coatings from carbamate chemistry. The review also focuses on the chemistry of PU, the importance of side products such as biuret, allophanate formation, as well as different low VOC PU coatings such as moisture-cured PU-urea, polyurea, PU-imide, UV cure and waterborne PU coatings. A brief description of functionalized dendritic/hyperbranched polymers, different monomers and synthetic approaches, and their use in the PU coating sector is addressed. In the context of nanostructuring, sol-gel chemistry to formulate ceramer coatings and use of functionalized nanomaterials in PU coatings is described. This portion also includes silica grafting and functionalization of nanosilica particles, polyhedral oligomeric silsesquioxane and the use of bridged polysilsesquioxanes in PU coatings. A wide variety of fillers, whiskers and fibers as well as clay and wollastonites with structural modification is described for use in nanocomposite PU coatings, with special emphasis on the latest development in PU-layered silicate nanocomposites. The use of different reactive-type organophosphorus compounds, aziridinyl curing agents in aqueous PU dispersions, phosphazenes, organo-boranes such as different carboranes for use in the formulation of flame retardant coatings is described. Since surface properties determine the resistivity of coatings towards corrosive chemicals, moisture and dirt repellency, a portion of the review will also be devoted towards modification of surface properties using fluoropolymer, and the synthesis and a brief description of the available fluorinated diols is given. (c) 2006 Elsevier Ltd. All rights reserved.