Lossen Reaction, Polymer Synthesis and Potential Applications of Latent Isocyanates

Isocyanates are of high interest for their versatile reactions and industrial uses in agrochemicals (e.g., herbicides) and polymers (e.g., polyurethanes and polyureas). The main objectives of this thesis research are to study the Lossen reaction of the N-acetoxy amide (AA) as a latent isocyanato group and explore potential applications of AA-containing compounds and polymers. Another objective is to develop a new method for optical sensing of isocyanates in air and as well nitroaromatic compounds.Study and applications of the Lossen reaction of a compound equivalent to an industrially important diisocyanate are described. The conversion of the AA group in a precursor monomer to the isocyanato group under various conditions was studied. In the presence of a polyol, polyurethanes or AA-terminated prepolymers could be formed, depending on the reaction conditions (e.g., temperatures and a base catalyst). In addition, the synthesis of AA-containing polymethacrylates and thermal conversion of the AA group to the reactive isocyanato group are illustrated. The AA-containing methacrylate monomer was prepared and polymerized with methyl methacrylate to form a series of copolymers with a range of the AA content. These copolymers were characterized by IR, 1H NMR and 13C NMR spectroscopy, thermogravimetric analysis, differential scanning calorimetry and gel permeation chromatography. Treatment of these copolymers at 110-130 °C led to the in situ formation of the isocyanato group and thus chemically reactive polymers.A fluorescence quenching method is introduced for direct and sensitive detection of various aliphatic and aromatic isocyanates in air. The high sensitivity is attributed to high fluorescence of polymer P1 film as a result of its unique aggregation-induced emission. The isocyanates can be detected at the ppt level typically within 10-60 s under ambient conditions. Moreover, the further application of fluorescent polymer P1 for sensing nitroaromatic compounds in air and in solution is explored. A large fluorescence quenching (98 %) was found for picric acid with a concentration of 4.7×10-6 M. In addition, 2,4-dinitrotoluene (DNT) at the ppb level in air could be detected within 60 s.