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

Abstract

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 de‐blocking 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. Copyright © 2007 Society of Chemical Industry

Preparation and Properties of Non-ionic Polyurethane Crosslinkers from 2-Ethoxyethanol/ϵ-caprolactam-Blocked Diisocyanate

“…In addition, we observed that the deblocking temperature obtained by TGA was different from that measured by DSC. This was due to differences in sample pans and thermal effects in these two instruments (1,10). Based on our study, the deblocking temperature measured by TGA was greater than that obtained by DSC measurement.…”

“…The onset of deblocking reaction has been determined by many analytical techniques (1,10,30). It should be noted that the reported deblocking temperatures frequently depend on the characterization technique, heating rate, and other variables.…”

“…However, conventional polyurethane coatings and adhesives contain significant amounts of volatile organic solvents and some contain free isocyanate monomers (9)(10)(11). The effects of volatile organic solvents on the environmental are detrimental and have led to an increased emphasis towards the development of water-borne polyurethane products, which provide eco-friendly systems.…”

Crosslinked polyurethane–epoxy hybrid emulsion with core–shell structure

“…The band at 1745 cm À1 was C=O stretching of the urethane group, and the strong band at 1223-1267 cm À1 corresponded to the stretching vibrations of C=O combined with NH in all the spectra. 28 The band at 1607-1606 cm À1 was benzene ring, the bands at 1533-1539 cm À1 correspond to carbamate, and the band at 2940-2926 and 2861-2853 cm À1 was asymmetric and symmetric C-H stretching of CH 2 , respectively. The absorption peaks of NCO at 2277 cm À1 and epoxide groups at 917 cm À1 also appeared in Fig.…”

Preparation and Characterization of Polyurethane Bioadhesive from Hydroxyl-terminated Polylactide and Imidazole-blocked Isocyanate

“…Commercial blocking agents include phenol, caprolactam, methyl ethyl ketoxime, amines, dimethyl pyrazoles, diethyl malonates, sodium bisulte and many others. [17][18][19][20] The rate and extent of deblocking reaction depend on many factors: the structure of isocyanate and blocking agent including substituents, solvents, catalysts, temperature and the thermal stability of the isocyanate-blocking agent bond.…”