In this study, we present a partially bio‐based, sustainable, environmentally friendly, and renewable bifunctional polybenzoxazine (PBZ), synthesized in accordance with green chemistry. Using bio‐derived precursors such as vanillin, 4‐hydroxybenzaldehyde, four types of bifunctional phenols were synthesized via acid‐catalyzed aldol condensation reactions. These phenols were then used to develop corresponding benzoxazine (BZ) monomers and their PBZs. The synthesized BZs and PBZs were characterized using FTIR, 1 H NMR, DSC, and TGA. Surface‐modified cotton fabric and mild steel (MS) were coated with the PBZs and analyzed by contact angle measurements, SEM, EIS, and Tafel plots. Among the materials tested, the poly(CP‐HB‐aptes) with 50% Si‐coated cotton fabric exhibited excellent performance, achieving a high water contact angle value of 149°, oil–water separation efficiency of 99.8%, and oil flux value of 19,243 L m −2 h −1 . Additionally, PBZ‐coated mild steel (MS) demonstrated superior anti‐corrosion performance with an inhibition efficiency of 95% and an impedance of 40.25 k Ω cm 2 based on EIS and Tafel analysis. The stability of the coated fabrics was further evaluated under harsh conditions including acid/alkaline immersion, mechanical abrasion, and UV/thermal irradiation. These results confirm the potential of developed PBZ coatings for diverse applications such as oil–water separation, emulsion separation, corrosion protection, and anti‐icing surfaces.