Low viscosity (meth)acrylates as reactive additives in reactive compositions for making rigid polyurethane/polyisocyanurate comprising foams

A method for making a polyisocyanurate (PIR) and/or a polyurethane (PUR) comprising rigid foam, the method comprising:

• combining and mixing:
• a) a polyisocyanate composition comprising one or more polyisocyanate compounds;
• b) an isocyanate-reactive composition comprising one or more isocyanate-reactive compounds;
• c) at least one catalyst compound suitable for making the polyisocyanurate (PIR) and/or the polyurethane (PUR) comprising foam;
• d) at least one blowing agent;
• e) acrylate and/or methacrylate compounds as a reactive viscosity reducer wherein the acrylate and/or methacrylate compounds comprise at least one first acrylate and/or methacrylate compound selected from cyclic trimethylolpropane formal acrylate (CTFA), 3,3,5-trimethyl cyclohexyl acrylate (TMCHA), isobornyl acrylate (IBOA), 4-tert-butylcyclohexyl acrylate (TBCHA), benzyl acrylate (BZA), phenol (EO) acrylate (PHEA), benzyl methacrylate (BZMA), phenoxyethyl methacrylate (PHEMA), tetrahydrofurfuryl methacrylate (THFMA), isobornyl methacrylate (IBOMA), and mixtures thereof and at least one second acrylate and/or methacrylate compound having no isocyanate-reactive groups and having 2 or 3 reactive acrylate groups or methacrylate groups and having a viscosity at 25° C.≤30 mPa·s;
• and optionally
• f) one or more surfactants, one or more flame retardants, one or more antioxidants, or combinations thereof;
• to form a reactive composition;
• and
• reacting the reactive composition in the absence of a thermal radical initiator to produce the PIR and/or PUR comprising rigid foam;
• and optionally,
• subjecting the PIR and/or PUR comprising rigid foam to a post foaming temperature treatment,
• wherein e) the acrylate and/or methacrylate compounds are polymerized by heat generated during the reaction of the reactive composition and during the optional post foaming temperature treatment.