Synthesis and characterization of isocyanate-functionalized hyperbranched polyurethane and its cocuring with benzoxazine

In the study, isocyanate-functionalized hyperbranched polyurethane (HPU  NCO ) with a degree of branch of 35.2% was synthesized via an A 2 + B 3 method. This novel HPU  NCO was used to fabricate a blend system with hydroxyl groups bearing benzoxazine precursor (BZ  OH ) to investigate its effective on the thermal properties of BZ  OH . The structure of HPU  NCO is confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance spectroscopy. The curing behavior of the reactive HPU  NCO /BZ  OH blend is investigated via differential scanning calorimetry and FTIR analyses. HPU  NCO /BZ  OH blend indicates two successively broad exotherm peaks centered at 132 and 204°C, respectively, which is obviously different from that of BZ  OH with one broad peak centered at 206°C. Thermogravimetric analysis results confirmed that the thermal stability was enhanced and the char yield of BZ  OH was increased from 34.3 to 43.2% by cocuring with 10 wt% HPU  NCO . POLYM. ENG. SCI., 55:604–613, 2015. © 2014 Society of Plastics Engineers