Alkyl sulfone bridged phosphorus flame-retardants for polypropylene

Three novel alkyl sulfone bridged phosphorus (P) compounds namely 6,6'-(sulfonylbis(ethane-2,1-diyl))bis (dibenzo[c.e][1,2]oxaphosphinine 6-oxide) (SEDOPO), sulfonylbis(ethane-2,1-diyl))bis(diphenylphosphine oxide) (SEDPPO), and tetraphenyl (sulfonyl bis(ethane-2,1-diyl)) bis(phosphonate) (SEDPP) (i.e. phosphine oxide, phosphinate and phosphonate, respectively) were synthesized via a Michael addition reaction with good yields (>= 85%) at a 200-g scale. They exhibited thermal stability above 250 degrees C, which allowed them to be melt-processed with polypropylene (PP) and formed into thin films (similar to 0.6 mm). Rheological measurements of the PP blends exhibited a typical shear thinning behavior and provided evidence for the synthesized compound's thermo-oxidative stabilizing effect. This was also confirmed by thermal analysis showing that the thermo-oxidative stability of PP-SEDOPO and PP-SEDPPO blends was higher (similar to 25 degrees C) than the blank PP: however, PP-SEDPP had a smaller impact. Small scale fire tests of the PP-FR blends confirmed the flame retardant efficacy of the new P-compounds. Cone calorimetiy on PP-SEDOPO blends showed a reduction in the heat release rate (HRR) (similar to 48%) compared to blank PP. Further thermal and evolved gas analysis of the PP blends confirmed that the new P-compounds are primarily active in the gas-phase. (C) 2021 The Author(s). Published by Elsevier Ltd.