Novel p-ethynyl-substituted rigid rod monomers were studied by pressure differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), isothermogravimetric analysis (IGA), and TGA-IR. These monomers, 4,4’-bis[((4-ethynylphenyl)carbonyl)oxy] designated 1, 1,5-bis[((4-ethynylphenyl)carbonyl)oxy]naphthalene, designated 2, and bis(4-ethynylphenyl)pyromellitimide, designated 3, were polymerized in the solid state. Thermal polymerization in Nz or air produced highly cross-linked resins with polymerization exotherms centered between 212 and 276 degrees C. The Delta H’s of polymerization of these resins in air were found to be double those in N-2. When monomers 1 and 2 were heated in air from 23 to 750 degrees C at 10 degrees C/min, the main decomposition product was carbon dioxide, evolving at a maximum rate between 500 and 600 degrees C; water was also detected as a decomposition product. Void-free neat resin moldings, designated 1p to 3p, were made by compression molding the monomers and then heating them. The resulting polymers were highly cross-linked, and their glass transition temperatures (T-g) were much higher than their polymerization temperatures. Using thermomechanical analysis (TMA), we found that polymers 1p to 3p had T-g’s of 422, 329, and 380 degrees C, respectively. The thermal and thermooxidative stabilities improved when 1p to 3p were postcured in N-2 (the postcured polymers were designated 1pp to 3pp). The linear thermal expansions (LTE) for 1p and 3p were 1% between 23 and 420 degrees C. Using theological analysis, we could not clearly detect the T-g’s of 1p to 3p because their moduli dropped only slightly between 23 and 490 degrees C and the changes in tan delta were very low. Because of high cross-link density, their moduli changed little as the resins went from a glassy to a robbery state. Their shear storage moduli in air ranged from 0.82 (3p, 3pp) to 1.6 GPa (1pp) at 23 degrees C, from 0.16 (2p) to 0.7 GPa (1 pp) at 380 degrees C, and from 0.18 (1pp) to 0.6 GPa (2p) at 490 degrees C, Finally, these novel p-ethynyl polymers exhibited an excellent combination of high T-g, low LTE, and high thermooxidative stability. Most notably, 3pp lost only 3% of its initial weight when it was aged for 500 h at 288 degrees C in air.