Polyhedral oligomeric silsesquioxane hybrided with DOPO and phenylboronic acid for flame-retarded epoxy resin

A new polyhedral oligomeric silsesquioxane (POSS) derivate bearing phenylboronic acid group and 6H-dibenzo[c,e][1,2]oxaphosphinine-6-oxide (DOPO) unit was synthesized and applied in flame retardant epoxy resin (EP). Compared to pure EP, EP/POSS-DOPO-(phenylboronic acid) composites had good transparency and better thermal stability. Micro-scale combustion calorimetry results showed that the addition of POSS-DOPO-(phenylboronic acid) hybrid could greatly reduce the PHRR and THR of EP/POSS-DOPO-(phenylboronic acid) composite. Simultaneously, the UL-94 of EP composite with 7% POSS-DOPO-(phenylboronic acid) achieved V-0 grade and the LOI value increased from 19.4% (neat EP) to 28.6%. Raman spectra results suggested that POSS-DOPO-(phenylboronic acid) hybrid enhanced the formation of residual char with graphitic structure during combustion. Besides, SEM characterization showed that the char of EP/POSS-DOPO-(phenylboronic acid) composite was much more continuous and compact in comparison with that of control samples. Moreover, the mechanical and dielectric properties of EP/POSS-DOPO-(phenylboronic acid) composites have been greatly improved for a better application.