Flame, smoke and toxicity retardant composition for use in polyurethane/polyisocyanurate comprising foams

A reactive mixture for making a polyisocyanurate and/or polyurethane (PIR/PUR) comprising material, said reactive mixture comprising:

• a fire retardant composition comprising:
• a) at least one compound having at least one ethylenically unsaturated moiety having a number average equivalent weight<160 g/mol, and
• b) optionally one or more radical initiator compound
• characterized in that the onset temperature for radical polymerization (Tonset) of the ethylenically unsaturated compound with or without the radical initiator is 2° C. up to 40° C. lower than the maximum reaction temperature achieved during the process for making the PIR/PUR material (reaction exotherm (Treaction)), and
• a polyisocyanate composition comprising one or more polyisocyanate compounds;
• and
• an isocyanate-reactive composition comprising one or more isocyanate-reactive compounds;
• and
• at least one catalyst compound suitable for making the PIR/PUR comprising material, and
• optionally one or more blowing agents;
• and
• optionally one or more surfactants, one or more antioxidants, or combinations thereof.