Toluene based polyurethane coatings

Up to this point we have discussed only carbamates la-4a with a single carbamate group on the phenyl ring as model systems for aromatic polyurethane photodecomposition. In polyurethane coatings based on the aromatic diisocyanate TDI two carbamate groups are attached to the phenyl ring. Furthermore commercially available TDI is actually a mixture of 2,4-toluene diisocyanate (2,4-TDI) and 2,6-toluene diisocyanate (2,6-TDI) which when formulated give 2,4- and 2,6-biscarbamates. Model systems for these species would then be biscarbamates of 2,4-TDI and 2,6-TDI (as shown below) and not carbamates such as la-4a. 

This subject was studied in relation to the silicone breast implant controversy of the 1990s. Silicone-fiUed artificial breasts were coated with thin layers of a TDI-based polyurethane foam to encourage stabilization by cell ingrowth. Residual toluene diamine (TDA) was found in prepolymer-based polyurethanes at the part-per-biUion level and, more importantly, hydrolysis that would lead to the release of more TDA in vivo was suspected. 

The most technologieally advaneed products are used for waterproofing and pipeline coatings. These products are also based on dispersion of asphalt in the above mentioned solvents but reinforced with addition of polymer. The addition of polymer modifies the plastie behavior of asphalt and renders it elastomeric. Additional solvents are usually added to improve the solubihty of polymerie eomponents. Reaetive polyurethanes are the most frequently used modifiers for waterproofing hquid membranes. Toluene and xylene are the... 

Figure 3.9 Reaction of polyethers with p-toluene sulfonic acid - gas chromatography. Gas chromatogram of reaction products of polyurethane polyethers (1) propylene glycol diacetate (2) glycerol triacetate (3) trimethylpropane triacetate (4) triethylanolamine triacetate (5) pentaerythritol tetracetate. Gas chromatographic conditions column 1 m x 3 mm, coated with 15% FFAQ on Uniport B, oven 170 °C chart speed 1 cm/s. (b) Gas chromatogram of reaction products of polyurethane polyethers based on amines (1) pyropylene glycol diacetate (2) derivative from 1,2 diaminoethane (3) derivative from 2,2 -diaminodiethylamine. Gas chromatographic conditions Column 1 m x 3 mm packed with 15% SE-30 on Uniport B oven 230 "C chart speed, 1 cm/min.

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