The present work provides a facile process route for the syntheses of pyrimidinone‐based benzoxazines by using stoichiometric quantities of pyrimidinone bisphenol (PBU) and paraformaldehyde, which are separately reacted with various types of amines under suitable experimental conditions. The molecular structure, curing characteristics, thermostability, hydrophobic behavior, and dielectric properties were analyzed using appropriate analytical methods. The polymerization temperature ( T p ) of monomers such as PBU‐oda, PBU‐cha, PBU‐ffa, PBU‐a, and PBU‐fa was determined by differential scanning calorimetry (DSC), and the T p values were noted at 205, 198, 203, 218, and 240°C, respectively. The percentage carbon residue at 850°C for poly(PBU‐oda), poly(PBU‐cha), poly(PBU‐ffa), poly(PBU‐a), and poly(PBU‐fa) were analyzed using thermogravimetric analysis (TGA). The water interface angle values for poly(PBU‐oda), poly(PBU‐cha), poly(PBU‐ffa), poly(PBU‐a), and poly(PBU‐fa) was found to be 141°, 134°, 142°, 136°, and 142°, respectively. The results from the dielectric studies indicate that the benzoxazines (PBU‐ffa and PBU‐a) composites reinforced with palm flower silica (PF‐SiO 2 ) and boron nitride‐g‐C 3 N 4 (BN‐g‐C 3 N 4 ) were found to be suitable for low and high dielectric applications. From these diverse studies, it can be determined that pyrimidinone‐based benzoxazines to be utilized as high‐performance products in the form of encapsulants, potting agents, and composites for automotive and microprocessor applications.