Synthesis and characterization of reactive blocked‐isocyanate coupling agents from methyl ethyl ketoxime, ethyl cellosolve/ε‐caprolactam blocked aromatic and aliphatic diisocyanates

Abstract

AbstractA series of water‐dispersible blocked polyisocyanates were synthesized from toluene 2,4‐diisocyanate (TDI), isophorone diisocyanate (IPDI), dimethylol propionic acid, methyl ethyl ketoxime (MEKO), ethyl cellosolve (EC), and ϵ‐caprolactam (CL). The physical properties, such as the viscosity, pH, and storage stability, of the blocked‐polyisocyanate adducts were measured. All aqueous dispersions of the blocked polyisocyanates showed good storage stability. The prepared blocked polyisocyanates were characterized by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, and thermogravimetric analysis techniques. The FTIR confirmed that the NCO groups of the original TDI and IPDI molecules were completely blocked by the blocking agents. The thermal analysis measurements revealed that both the blocked TDI‐ and IPDI‐based polyisocyanates started to deblock at about 55–85°C. Compared to the CL‐blocked polyisocyanates, the MEKO‐ and EC‐blocked polyisocyanates had lower thermal dissociation temperatures and faster deblocking rates. We also found that the initial deblocking temperatures of the TDI‐based adducts were lower than those of the IPDI‐based adducts. The water resistance and tensile properties of the composite films from the blocked‐polyisocyanate crosslinkers and hydroxyl–polyurethane emulsion (HPUE) matrix were studied. The tensile strength increased and the elongation at break were lower in the composites compared to the pure HPUE film. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011