Synthesis and characterization of fluorinated polyurethane containing carborane in the main chain: Thermal, mechanical and chemical resistance properties

In this study, two fluorinated polyurethanes (FPU) containing carborane groups in the main chains were firstly designed and synthesized via the reaction of hexamethylene diisocyanate trimer (HDI trimer) with fluorinated polyesters (CFPETs) having hydroxyl-terminated carborane groups at room temperature. The structures of carborane fluorinated polyesters (CFPETs) and polyurethanes (CFPUs) were characterized by gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR) measurements. The thermal stability, mechanical properties, Shore A hardness, solvent resistance and acid-alkali resistance of the carborane fluorinated polyurethane films were also studied. Thermogravimetric analysis (TGA) tests manifested that the introduction of carborane groups into the main chain of fluorinated polyurethane endowed the obtained fluorinated polyurethane with excellent thermal stability. The thermal decomposition temperature of carborane fluorinated polyurethane (CFPU) increased by 190 °C compared with that of the carborane-free fluorinated polyurethane (FPU). Even at 800 °C, CFPU showed the char yield of 66.5%, which was higher than that of FPU (34.3%). The carborane-containing fluorinated polyurethanes also showed excellent chemical resistance and prominent mechanical property even after the cured films being immersed into Jet aircraft oil or 37% HCl for 168 h or at high temperature (700 °C). It is found that the structural characteristics of carborane group and the compacted structure of CFPU effectively improve the thermal stability, mechanical property, solvent resistance and acid-alkali resistance of the carborane-free fluorinated polyurethane. These excellent properties make CFPU as the useful raw materials to prepare the high temperature resistant coatings or adhesives for automotive engines, engine or fuel tank of aircraft and other equipment working in high-temperature or high concentrations of acid-alkali environments.