Synthesis and effects of waterborne polyurethane composite WPU/SAN for decreasing the sensitivity of hexanitrohexaazaisowurtzitane

The waterborne polyurethane composite (WPU/SAN) was prepared by seeded emulsion polymerization. The waterborne polyurethane (WPU) was previously synthesized from isophorone diisocyanate (IPDI), polypropylene glycol (PPG), dimethylolpropionic acid (DMPA) and 1, 4-butanediol (BDO) by a two-step process. Styrene (S) and acrylonitrile (AN) were subsequently added to the seed emulsion comprising the WPU previously synthesized to yield the composite WPU/SAN. Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction spectroscopy (WAXD) were utilized to characterize the products films. The results indicated that amorphous products were obtained as expected. The product composites were utilized to coat hexanitrohexaazaisowurtzitane (HNIW), and the characteristic height H50 of HNIW coated with the composite was improved from 13.6 cm to 30.4 cm, which is close to that of pure waterborne polyurethane. Besides, the coating results were observed using scanning electron microscopy (SEM), and the micrographs revealed that grains of HNIW crystal held together by small amounts of the composite WPU/SAN. The mechanism of the effects to decrease the sensitivity of HNIW was discussed according to the "hot spots" principle and the composite molecular structure.