Synthesis,characterization and thermal dissociation of 2-butoxyethanol-blocked diisocyanates and their use in the synthesis of isocyanate-terminated prepolymers

摘要

A series of blocked diisocyanates has been synthesized from toluene diisocyante (TDI),isophorone diisocyanate (IPDI),hexamethylene diisocyanate (HDI),4,4'-diphenylmethane diisocyanate (MDI) and 2-butoxyethanol.The synthesis of blocked diisocyanate adducts was confirmed by Fourier transform infrared,~1H NMR,electron impact mass spectrometry and nitrogen analysis.Differential scanning calorimetry (DSC),thermal gravimetric analysis (TGA) and carbon dioxide evolution were used to determine the minimum deblocking temperatures.De-blocking temperatures determined by these three techniques were found to be in the order DSC > TGA > CO2 evolution.The effect of different metal catalysts on thermal de-blocking reaction of the blocked diisocyanates was studied,using the carbon dioxide evolution method.It was found that iron(III) oxide has the maximum catalytic activity on de-blocking.The solubility of the blocked diisocyanate adducts was determined in different solvents.The study revealed that at 30 °C blocked IPDI and HDI adducts show better solubility than adducts based on TDI and MDI.Isocyanate-terminated prepolymers of blocked diisocyanates and hydroxyl-terminated polybutadiene (HTPB) were prepared.The storage stability and gelation times of the prepolymers were studied.Results showed that all the diisocyanate-HTPB compositions are stable at 50 °C for more than three months.However,aliphatic diisocyanate-HTPB compositions require greater gelation time than aromatic diisocyanate-HTPB compositions at their respective de-blocking temperatures.