In the present work, an attempt has been made to develop flexible, partially bio-based polybenzoxazine matrices with superhydrophobic behaviour for improved oil-water separation, self-cleaning and anti-corrosive properties. A new type of card-bisphenol (COBP) has been synthesized using cardanol and octanaldehyde as eco-friendly, natural precursors to substitute fossil-based materials to maintain environmental sustainability. Four distinct benzoxazines (COBP-oa, COBP-dda, COBP-oda, and COBP-fa) were synthesized using COBP and different types of amines viz., octylamine (oa), dodecylamine (dda), octadecyl amine (oda) and furfurylamine (fa) with paraformaldehyde through Mannich condensation reaction. The non-polar nature of these long aliphatic chains present in the benzoxazine molecules contributes to an enhanced superhydrophobic behaviour. Structural characterization of the synthesized monomers was confirmed through FT-IR and 1H NMR spectroscopic analyses. DSC analysis infers that the curing temperature of benzoxazine monomers is increased with increasing the aliphatic chain length. Data from TGA ascertain that the poly (COBP-fa) exhibited the highest thermal stability and char residue, among the synthesized polybenzoxazines (PBZs). The COBP-oda possesses a higher value of water contact angle of 155° which in turn contributes to superhydrophobic behaviour. The superhydrophobic behaviour also contributes to superior corrosion resistance, with an inhibition efficiency of 95.87 %. Further, it was also observed that the PBZ-coated cotton fabric achieved an oil-water separation efficiency of >90 %. The oil-absorption properties of the PBZ-modified foams showed 96–99 % oil absorption efficiency. Data obtained from different studies ascertain the versatility of the developed materials and suggest their utility towards high-performance coating applications, under adverse environmental conditions.