Novel phosphorus-nitrogen-silicon copolymers with double-decker silsesquioxane in the main chain and their flame retardancy application in PC/ABS

Summary Two novel phosphorus-nitrogen-silicon copolymers (DDSQ-N-P-yne and DDSQ-N-P-ene) were synthesized by hydrosilylation reaction with DDSQ and DOPO derivatives. DOPO derivatives with different end groups were designed and synthesized to compare the flame retardancy and compatibility of phosphorus-nitrogen-silicon copolymers by different linkers between DDSQ and DOPO derivatives. The synthesized copolymers have been evidenced by 1 H, 29 Si nuclear magnetic resonance, and gel permeation chromatography and then introduced into polycarbonate (PC)/acrylonitrile butadiene styrene (ABS) alloy to study their flame retardancy and explore whether they exhibit a synergistic effect on the flame retardancy. The flame-retardant properties of DDSQ-N-P-yne (or ene) systems as well as the morphology were investigated in detail by using limiting oxygen index, thermogravimetric analysis, UL-94, microcalorimeter, energy dispersive X-ray, and scanning electron microscopy, respectively. When DDSQ-N-P-yne (or ene) content is 10 wt%, the composites of PC/ABS are identified to be very effective according to limiting oxygen index, UL-94, and microcalorimeter. The microstructures of the char were investigated by scanning electron microscopy, and the results indicated a tight and compact graphitized layer shaped, which plays an important role in improving the excellent thermal stability and flame retardancy of PC/ABS alloy.