Nonisocyanate Based Polyurethane/Silica Nanocomposites
There is a growing intense effort to develop new chemical processes using natural resources due to the prediction that the petroleum resources will be exhausted within the next century.1 One such resource of particular interest is CO2, a nontoxic, nonflammable, naturally abundant carbon feedstock. Chemical addition of CO2 into valuable organic compounds is useful in the terms of both resource utilization and pollution prevention.2 One of the most promising methodologies in this area is the direct synthesis of carbonates via coupling of CO2 with epoxides under supercritical conditions.
Cyclic carbonates have been widely used as polar aprotic solvents, intermediates for organic and polymeric synthesis, and ingredients for pharmaceutical/fine chemicals in biomedical applications.3 Many organic and inorganic compounds, such as metal oxides, quaternary ammonium salts, transition metal complexes, and ionic liquid, have been developed to be used as catalysts for the cycloaddition of carbon dioxide with epoxides for the synthesis of cyclic carbonates.4 From the standpoint of environmental protection and resource utilization, the development of an environmentally benign process using carbon dioxide, which is the largest single source of greenhouse gas, could be utilized in the nanocomposite synthesis that uses cyclic carbonates as intermediates for the production of polyurethane polymers. Polyurethane polymers are used world-wide on a large scale for foam, fiber, adhesive and coating applications so forth. The involvement of toxic components, such as isocyanates, in their fabrication process makes the production extremely toxic and dangerous. More recently, non-isocyanate polyurethanes were formed by the reaction of cyclocarbonate oligomers and primary aliphatic amine oligomers.5 Among many studies, the reaction of oxiranes and CO2 to provide the five-membered cyclic carbonate has received much attention because of its simple reaction, high yield and harmless nature of the reagents. Our current research includes optimization studies on cyclic carbonate synthesis from epoxides by the use of supercritical carbon dioxide both as a medium and as a raw material, and synthesis and modification of silica nanoparticles, as different parts of a comprehensive work on development of environmental-friendly polyurethane/silica nanocomposite coatings with superior thermal and mechanical properties and also excellent fire retardance ability.
Preparation of Surface Modified Silica Nanoparticles with Supercritical Carbon Dioxide Ö. Malay, Y. Z. Menceloglu, N. Kayaman-Apohan, V. Kahraman and A. Gungor, MRS Fall Meeting Nov 27-Dec 1, 2007 Boston-USA.
Ö. Malay, O. Bayraktar, A. Batıgün, Complex coacervation of silk fibroin and hyaluronic acid, International Journal of Biological Micromolecules, Vol.40, 387-393, 2007.
B.B. Pekşen, C. Üzelakçil, A. Güneş, Ö. Malay, O. Bayraktar, A novel silk fibroin-supported catalyst for hydroxylation of phenol, Journal of Chemical Technology and Biotechnology, Vol. 81, 1218-1224, 2006.
O. Bayraktar, Ö. Malay, Y. Özgarip, A. Batıgün, Silk fibroin as a novel coating material for controlled release of theophylline, European Journal of Pharmaceutics and Biopharmaceuticals, Vol. 3, 373 – 381, 2005.
Ö. Malay, O. Bayraktar, A. Batıgün, pH-induced silk fibroin-hyaluronic acid polyelectrolyte complexes. Part I. Swelling characteristics and iontophoretic drug delivery applications, submitted.