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This work reports on the thermal stability and flammability of a novel class of rigid polyurethane foams chemically modified by functionalized 1,2-propanediolisobutyl POSS (PHI-POSS) as a pendant group and octa (3-hydroxy-3-methylbutyldimethylsiloxy) POSS (OCTA-POSS) as a chemical cross-link. The foamed hybrid materials were prepared in a three-step process using a sorbitol-based polyether polyol, polymeric 4,4 0 -diphenylmethane diisocyanate and dimethyl propane phosphonate as a flame retardant. The addition of the POSS modifier influences the PU cellular structure as evidenced by a change in anisotropy index of the cross section parallel to the growth direction. Based on thermogravimetric data and flammability results, one can suggest that there is char formation at the surface and the formed layer acts as an insulating barrier limiting heat and mass transfer with flame retardant and thus leading to decreased heat release rate, especially for systems containing OCTA-POSS.

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