Copolymerization of mono and difunctional benzoxazine monomers with bio-based phthalonitrile monomer: Curing behaviour, thermal, and mechanical properties

The eugenol based phthalonitrile (EPN) monomer was successfully copolymerized with mono and difunctional benzoxazine (P-a and BA-a) monomers via concerted catalysis polymerization. The loading of EPN in benzoxazine monomers was varied from 10 to 40 wt% and impacts of loading on thermal, thermomechanical and mechanical properties were studied. The FTIR analysis confirmed that both poly(P-a/EPN) and poly(BA-a/EPN) copolymers can be completely cured without the addition of curing additive. The addition of the bio-based EPN monomer enhanced the curing peak temperatures and reduced the curing reaction enthalpies. Initially, OH groups were produced from the oxazine ring opening polymerization of benzoxazine and they enhanced the curing of EPN. The thermal stabilities, as well as the stiffness and Tg of the copolymers, were much higher as compared to the neat polymers. Highest values were seen on the 40 wt% loading of EPN monomer in the copolymers. Moreover, the difunctional benzoxazine based copolymer showed higher enhancements in the properties as compared to the mono-functional benzoxazine based copolymer. The decline was seen in the flexural properties as EPN monomer contains the flexible chain in the structure. The morphological changes supported all the claims for the copolymers. The prepared copolymers can be used as a high performance thermosetting resin.