Poly(benzoxazine-co-urea): A Solventless Approach Towards The Introduction of Alternating Urea Linkages In Polybenzoxazine

Abstract

In this paper, an alternative approach towards synthesis of phenolic/urea copolymers has been explored via benzoxazine chemistry. Biobased poly(benzoxazine-co-urea) has been prepared through ring opening polymerisation of a benzoxazine monomer containing urea linkages. The amine co-reactant for the benzoxazine synthesis was derived by the additive rearrangement of 4,4′-methylenebis(phenyl isocyanate) (MDI) with ethylene diamine, which underwent Mannich like condensation with cardanol and paraformaldehyde to yield biobased benzoxazine monomer containing urea linkages. The structure of the amine and the benzoxazine has been characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (1H-NMR). Benzoxazine monomer undergoes thermally accelerated ring opening polymerization to form cross-linked networks, which has been demonstrated using rheometry and non-isothermal differential scanning calorimetry (DSC). The presence of alternating urea linkages in the benzoxazine network is expected to improve the adhesive properties of the resin, which was quantified in terms of Lap shear strength. Thermal degradation of the crosslinked copolymer has also been studied by thermogravimetric analysis (TGA).