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

Abstract

One package heat curable polyurethane system typically requires blocked isocyanates with a relatively low deblocking temperature. In this study, a series of new aromatic secondary amines blocked polymeric methylene diphenyl diisocyanate (pMDI) was synthesized and characterized. Hot-stage FTIR, DSC and TGA spectroscopic methods were used to determine the deblocking temperatures of the blocked isocyanates. Cure reaction between the blocked isocyanates and a commercial polyl (PPG-2000) were carried out to establish structure and property relationship. Deblocking temperature and gel time of the blocked isocyanates based on N-methylaniline and N-methyl-o-toludine were lower than the blocked isocyanates with imidazole and methyl 4-methylaminobenzoate. Unexpected high deblocking temperature of imidazole and methyl 4-methylaminobenzoate was due to intra molecular hydrogen bonding. Solubility behavior of the blocked isocyanates was also studied using a series of polyols (PEG-400, Terathane-2000, PPG-2000, and castor oil).

Multifunctionalized Cellulose Nanofiber for Water-Repellent and Wash-Sustainable Coatings on Fabrics

“…SEM analysis shows that AMT only partially coated on the cloth. On the other hand, for the MMT coatings (Figure d), the isocyanate groups on MMT build carbamate linkage with hydroxyl groups on the cotton cloth during the coating process; ,, therefore, a smooth MMT coating is formed over the cotton fiber surfaces.…”

Nanocellulose-Based Thermoplastic Polyurethane Biocomposites with Shape Memory Effect

“…Along with aliphatic TPU, aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate (MDI), 2,4-toluylene diisocyanate (TDI), and cycloaliphatic isophorone diisocyanate (IPDI) may be used for the synthesis of TPUs. The symmetrical structure of the aromatic MDI is such that a strong degree of phase separation is achieved between the soft and hard segments, especially at low temperatures [110]. This leads to a regular morphology and consequently high mechanical and adaptive properties of polyurethane materials.…”

Blocked isocyanates: from analytical and experimental considerations to non-polyurethane applications

“…When investigating imidazole blocked poly(MDI) FTIR analysis produced a deblocking temperature of 170°C, considerably lower than that produced by TGA (216°C) and 120°C lower than that produced by DSC (291°C). 64 Furthermore, Gedan-Smolka et al reported differences in deblocking temperature when probing hydroxybenzoic acid ethyl ester blocked HDI. Analysis using FTIR afforded a deblocking temperature of 118°C, yet analysis using simultaneous thermal analysis coupled with a quadrupole mass spectrometer (STA-QMS) revealed three deblocking temperatures (DSC/TGA = 150°C, DSC = 170°C and MS = 155°C), all of which were significantly higher than that produced by FTIR.…”

“…Imidazole/imidazoline Imidazole 64,86 Basicity of imidazole able to accelerate the blocking reaction without additional catalyst. 22 Large substituent effect on deblocking temperature.…”

“…57,115 Catalysts It should be noted that for the synthesis of blocked isocyanates, no catalyst is necessary in the majority of instances, with Sankar and Yan noting that the aromatic secondary amines present in their system were sufficiently reactive without the addition of a catalyst. 116 In spite of this, dibutyltin dilaurate (DBTL) is frequently used to ensure both a successful reaction and that the reaction goes to completion, with catalysis proposed to proceed via a four-membered transition state. 117 One system that often does require the use of a catalyst is the production of uretdiones.…”