Abstract
A novel halogen-free flame retardant (6,6′-(((methylenebis(4,1-phenylene))bis(azanediyl))bis((4-hydroxy-3-methoxyphenyl)methylene))bis(6H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide)(DP-DDM))) was synthesized via a one-pot procedure based on the Pudovik reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide and imine directly resulting from 3-methoxy-4-hydroxybenzaldehyde with 4,4′-methylenedianiline (DDM). The thermal curing behaviors of epoxy resins with different contents of DP-DDM were investigated by differential scanning calorimetry under a nonisothermal condition, aimed to suggest an optimized curing procedure in accordance with the property of DP-DDM. These DP-DDM-modified epoxy thermosets under optimized curing procedure showed high glass transition temperature and thermal degradation activation energy. Moreover, their high flame-retarding performance has been found: the epoxy thermosets with a relatively low addition amount of DP-DDM (on account of the phosphorus content of 0.75 wt%) can reach UL 94 V-0 (Instrumental analysis and measurements) rating with limiting oxygen index value of 34.5.
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