Blocking and Deblocking of Diisocyanate to Synthesize Polyurethanes

Abstract

Diisocyanates, particularly toluene diisocyanate (TDI), are useful for the preparation of various polyurethanes with specific applications as leather-like materials, adhesives and insoles, etc. Blocking agents can be used for the operational simplicity and to reduce the hazards of TDI. In this paper, we reported the use of 3-(4-bromo-phenyl)-1H-pyrazole to block toluene diisocyanate (TDI). FTIR, NMR, thermogravimetric analysis, contact angle analysis and differential scanning calorimetry (DSC) were used for the characterization. The effectiveness of the blocking was confirmed by spectroscopic techniques. The DSC thermogram showed that blocked adducts deblock at 240 °C, causing the regeneration of TDI, and causing the diisocyanates to react with polyols of different molecular weights, forming polyurethanes. The characterization of the polyurethanes was performed by infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric analysis, differential scanning calorimetry and a contact angle study.

A simple method to enhance the interface properties of carbon fibre/polyamide 6 composites: Grafted caprolactam-blocked 3-isocyanatopropyltriethoxysilane on carbon fibre surface

“…In step 2, the sample shows a thermal weight loss of 36.14%, and the DSC curve exhibits an obvious endothermic peak (P1). Since the unblocking temperature of the CPL-blocked -NCO group is generally between 130-250°C, the mass and energy change of step 2 is mainly caused by the unblocking of the C 3 IPTS terminal group [38,44,45]. In other words, the CPL of C 3 IPTS is released at this stage, and the -NCO group is exposed.…”

Transition metal-catalysed carbene- and nitrene transfer to carbon monoxide and isocyanides

“…In polymer chemistry blocked isocyanates are an active domain of contemporary research to avoid using diisocyante monomers and hereby reduce the hazards of isocyanates. 63 Iron. This is one of the most abundant base-metals on Earth, 64 making its utilization highly interesting from an economical as well as ecological point of view.…”

“…In polymer chemistry blocked isocyanates are an active domain of contemporary research to avoid using diisocyante monomers and hereby reduce the hazards of isocyanates. 63 …”

Synthesis of Polyurethanes Through the Oxidative Decarboxylation of Oxamic Acids: a New Gateway Toward Self-blown Foams

“…[25] The most representative examples are phenol, [28] oxime [29] and pyrazole. [30] The isocyanate is then regenerated at high temperature (typically 100 °C ≤ T ≤ 200 °C) through the reverse reaction (Figure 1a). Despite the high industrial applicability of this approach, notably for the design of one-pot formulation used in coating applications, it still relies on the use of free isocyanates for the synthesis of the blocked precursors.…”