SummaryPhosphorus-containing epoxides were used to generate several oligomeric polyether diols, which were in turn utilized in the preparation of model polyurethane (PU) samples, either as comonomers in the polymerization (Prep samples) or solvent blended into a priori prepared PU (Blend samples). The resultant samples were evaluated for heat release reduction potential using microcombustion calorimetry. Several variables were investigated in the oligomerization of the original epoxides, such as presence of initiator, epoxide comonomer, and solvent. The oligomer mixtures were thoroughly characterized, using NMR, mass spectrometry (MS), elemental analysis, and viscosity measurements. The final PU Prep samples were carefully analyzed to demonstrate and evaluate the degree of chemical incorporation of the polyether diols into the PU main chain.Results from the heat release studies demonstrated that incorporation of the phosphoruscontaining diol did lower flammability, but the structure of the original epoxide, as well as the oligoimerization conditions, had an effect on heat release reduction. The results are complex and require further study, but the phosphonate-based materials showed greater heat release reduction potential, both in the form of Prep and Blend samples, especially in one case of a Blend sample, where a notable amount of intumescent char was formed. KEYWORDS epoxides, flame retardancy, flammability testing, oligomers, phosphorus, polyurethanes 1 | INTRODUCTION Polyurethane (PU) foams, especially flexible foams, remain one of the largest fuel loads in the modern home. 1 These foams, should they ignite, can and will lead to catastrophic fire losses because of room flashover events. 2 While flame retardants are available for use today to lower the fire risk of PU foams, some of these flame retardants of small molecular size have been found to have environmental persistence issues, as well as negative bioaccumulation and toxicity profiles. 3 Further, the use of additives presents its own problem in that a small molecule flame retardant not chemically bound (through covalent bonds) to the PU matrix can slowly leach out over time, resulting in a loss of fire safety performance during the lifetime of the PU foam.There have been some attempts to address the additive issue by going to higher molecular weight/size molecules, such as oligomeric and polymeric flame retardants, which, should they migrate out of a polymer, present less of a bioaccumulation hazard. Still, what is mostly available for PUs today are small molecule flame retardant additives. The list of drawbacks of small molecule flame retardant additives leaves 3 other solutions (other than the use of sprinklers) that a fire protection engineer can use: barrier fabrics, conformal coatings, and reactive flame retardants.Barrier fabrics are currently being studied as a solution/replacement for flame retardant additives, but, these fabrics have their own drawbacks including fabrication issues, costs, and inability to protect against fire when the b...