Study on synthesis, characterizations, and properties of pyridinol-blocked isocyanates and waterborne polyurethane
A series of pyridinol-blocked isophorone isocyanates were synthesized through esterification reaction, Fries rearrangement, and blocking reaction and characterized by 1H-NMR, 13C-NMR, and Fourier transform infrared spectra. Based on the synthesized blocked isocyanates, the blocked waterborne polyurethane (BWPU) was prepared by the self-emulsification method. The deblocking studies revealed that the deblocking temperature reduces with electron-withdrawing and steric hindrance substituents on the ortho position of pyridinol. The stability, molecular weight (Mw), particle size, viscosity, and hydrophilicity of BWPU were studied and compared. The results showed that with an increased amount of blocking agents, molecular weight, particle size, and viscosity decrease and the hydrophilicity increases.