<p>Polybenzoxazines (PBZs) are advanced thermosetting resins whose properties can be tuned by functional group substitution. In this study, the curing behaviors of bisphenol A-based benzoxazine monomers functionalized with nitrile and ethynyl groups at the ortho, meta, and para positions of the amine group were compared. Differential scanning calorimetry (DSC) revealed that nitrile substitution increased the onset and peak curing temperatures as well as the activation energy, thereby delaying the curing process. In contrast, ethynyl substitution significantly lowered these parameters, indicating a barrier-lowering effect that accelerates crosslinking. In situ FT-IR at 160&#xa0;°C (air) confirmed slower ring-opening polymerization; nitrile conversion was minimal at this early stage, while ethynyl groups actively contributed to network formation. For nitrile-functionalized monomers, ortho, and para substitutions most severely hindered curing, whereas for ethynyl-functionalized monomers, meta-ethynyl provided the best balance when evaluated by lower <i>E</i>_a and higher network density. The results show the opposite directive influences of nitrile and ethynyl groups, which can serve as guidelines for controlling PBZs toward advanced thermal, structural, and electronic applications. All comparisons refer to identical early-stage FT-IR conditions (160&#xa0;°C, air) and DSC-derived <i>E</i>_a; high-temperature trimerization of nitrile groups is discussed as a separate operating window.</p>