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

Abstract

A 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 e-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 ANCO 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 MEKOand 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.

Mechanical and thermal properties of eucalyptus fiber composites bonding by blocked polyurethane adhesive

“…EC‐blocked polyisocyanate (EC‐bp) and hydroxyl‐terminated polyurethane emulsion (PU) were prepared in our lab. They were prepared according to the procedure reported in our previous work 22. The maximum deblocking temperature was around 150°C.…”

Application of blocked isocyanate in preparation of polyurethane(urea) elastomers

“…Duplicate experiments were conducted for each set of mixture to ensure the accuracy of the collected data. 51 2.3.9 | Atomic force microscopy…”

“…According to literature reports, the storage time at room temperature can even reach 6 months. 51 In the presence of a suitable co-reactant, BPUP was unblocked when heated, and then the chain extension reaction was allowed to proceed. Finally, polyurethane materials with better properties were obtained by casting molding process.…”

Synthesis and Deblocking Studies of Low Temperature Heat-Curable Blocked Polymeric Methylene Diphenyl Diisocyanates

“…It has been shown that structures of blocking agents and isocyanates equally have a strong influence on deblocking temperature (1,(15)(16)(17). Several compounds, having active hydrogen atom, have been reported as blocking agents, including phenols, oximes, amides, imides, imidazoles, amidines, pyrazoles, N-methyl anilines, and active methylene compounds (1,2,(15)(16)(17)(18)(19)(20)(21). It has been reported that substituent present in the blocking agent has a very strong influence on the deblocking temperature.…”