A new thermo set system based on cardanol benzoxazine and hydroxy benzoxazoline with lower cure temperature

This paper describes the synthesis and characterization of a new curing system consisting of mono functional benzoxazine based on cardanol and hydroxyl functionalized benzoxazoline, where the phenol hydroxyl group acts both as a catalyst for the ring opening reaction of benzoxazine as well as oxazoline ring. The curing initiation temperature of cardanol benzoxazine was reduced to 138 °C from 230 °C with incorporation of hydroxy benzoxazoline (HBO). The heat of polymerization value has increased with incorporation of hydroxyl benzoxazoline up to 50 mol.%. The activation energy of cardanol benzoxazine has reduced initially with incorporation of hydroxyl benzoxazoline and later increased with respect to composition of monomers in the mixture. The flexible cardanol benzoxazine polymer displayed a lower storage modulus of 2.7 × 108 [pa] and a tan δ of 104 °C. The copolymers exhibited significant enhancement in these values with incorporation of hydroxyl benzoxazoline. The width of tan δ peak of copolymers also increased suggesting enhancement of toughness.

► A copolymer system was developed based on cardanol benzoxazine and hydroxy benzoxazoline monomers.
► In this new curing system hydroxy benzoxazoline monomer acted as a catalyst and reduced onset of curing.
► Incorporation of hydroxy benzoxazoline improved the mechanical properties as well as glass transition temperature of copolymers.