In this article, the syntheses and thermal properties of several alkyne- and phosphorus-containing materials are discussed. The materials were synthesized using substituted phenolic molecules which were added to phosphorus oxychloride. The materials synthesized include phosphine oxides, phosphates, diphosphates, and oligophosphates. The thermal properties of the synthesized materials were studied using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). In general, the DSC and TGA data showed that synthesized materials containing alkynes and phosphorus had good-to-excellent thermal stability with high-onset decomposition temperatures. Materials with a high alkyne-to-phosphorus ratio showed the highest char yields. DSC data showed crosslinking events for the alkynes and the phosphorus moieties. DSC also showed that the alkynes crosslinked at lower temperatures than the phosphates. Based on the TGA and DSC data of the alkyne-containing phosphorus materials, alkynes generally appeared to be better char-inducing groups than was phosphorus. The materials were blended into polycarbonate and tested for ignition resistance using the UL-94 flame test. In two cases, these halogen-free compounds, with their dual alkyne/phosphorous crosslinking mechanisms, are condensed-phase flame retardants that can be easily blended into polycarbonate at 10 wt % loadings to afford blends that give a UL-94 V-0 rating.