A facile approach to prepare cage-ladder-structure phosphorus-containing amino-functionalized POSS for enhancing flame retardancy of epoxy resins

The cage-ladder-structure phosphorus-containing amino-functionalized polyhedral oligomeric silsesquinoxanes (CLNH 2 -POSS) have been synthesized through a facile catalyst-free hydrolytic condensation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-vinyltrimethoxysilane (DOPO-VTMS) with 3-aminopropyl trimethoxysilane (KH540). The successful preparation of CLNH 2 -POSS has been proven by the characterization of Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy ( 1 H-NMR, 29 Si-NMR), matrix-assisted laser desorption ionization time of flight (MALDI-TOF), and X-ray diffraction (XRD). Then flame retardant (FR) epoxy resins (EPs) were prepared by the addition of different content of CLNH 2 -POSS into EPs with thermal curing technology. The CLNH 2 -POSS showed good solubility in EP matrix. The well-dispersed CLNH 2 -POSS contributed to thermal, mechanical, and FR properties of EP. Dynamic scanning calorimetry nonisothermal curing scans showed that CLNH 2 -POSS had accelerating effect on the curing of EP. With the addition of only 3 wt% CLNH 2 -POSS (0.30% phosphorus loading), the limiting oxygen index value of the EP composite increased from 25.5 of pure EP to 31.8, and vertical burning (UL-94) V-0 ratings was achieved. In addition, the EP composites showed improved thermal and mechanical properties. The investigations on char residue and pyrolysis volatiles of cured EP further revealed that CLNH 2 -POSS exerted FR effects in condensed and gas phase simultaneously.