Abstract: Four phenylethynyl-phthalimide-functionalized benzoxazine monomers were designed and synthesized. By adjusting the attachment position of phthalimide on the aromatic ring of benzoxazine and the substituent structure at the nitrogen site of the oxazine ring, the effects of molecular structure on the thermal-polymerization behavior of monomers and the properties of cured resins were investigated. The chemical structures of the monomers were characterized by Proton Nuclear Magnetic Resonance（¹H-NMR）, Carbon-13 Nuclear Magnetic Resonance（¹³C-NMR） and Fourier-transform infrared spectroscopy (FT-IR). Differential scanning calorimetry (DSC), curing-kinetics analysis and in-situ FT-IR were employed to explore their thermal-polymerization behaviors. The results demonstrated that 2-(3-(furan-2-ylmethyl)-3,4-dihydro-2H-benzo e1,3 oxazin-8-yl)-5-(phenylethynyl) isoindoline-1,3-dione (oPP-pe-fa) possessed the lowest curing-peak temperature (227 ℃). Combined with the apparent-activation-energy results and in-situ FT-IR spectra, both the phthalimide attachment position and the N-side-chain structure could affect the thermal-polymerization behavior of monomers. Moreover, both the ring-opening reaction of oxazine rings and ethynyl-group reaction participated in the curing process. Furthermore, thermogravimetric analysis (TGA) was carried out to evaluate the thermal stability of cured resins. All benzoxazine resins possessed excellent thermal stability whereas obvious discrepancies existed among samples with different molecular structures. Among them, poly(2-(3-(3-ethynylphenyl)-3,4-dihydro-2H-benzo e1,3 oxazin-8-yl)-5-(phenylethynyl) isoindoline-1,3-dione) (poly(oPP-pe-ma)) containing a di-ethynyl structure exhibited optimal thermal stability and a char yield of 72 %. The flame-retardant performance was further assessed by the UL-94 vertical burning test, and poly(oPP-pe-ma) reached a UL-94 V-0 rating. These findings reveal that the phthalimide attachment position and N-substituent structure on the oxazine ring exert remarkable influences on the thermal-polymerization behavior of this kind of benzoxazine as well as the performance of cured resins, which provides a reference for the molecular-structure design of high-heat-resistant benzoxazine thermosetting resins.