Reaction-Induced Liquid Crystalline Polybenzoxazine Bearing Aromatic Amide Side Branches

In this study, a nematic phase structure is incorporated into polybenzoxazine to increase its thermal conductivity. A simple route for the synthesis of a thermally conductive polybenzoxazine containing liquid crystalline (LC) structure by grafting oligomeric p-sulfophenylene-terephthalamide (PSTA) is offered. Benzoxazine monomer of pHBA-da is synthesized via Mannich reaction of p-hydroxy benzoic acid, p-formaldehyde, and dodecyl amine. After ring-opening polymerization, the oligomer benzoxazine of OBZ─COOH is obtained. The OBZ─COOH/PSTA mixture is prepared by mixing PSTA with OBZ─COOH. Afterward, the grafted copolymer is named OBZ─PSTA copolymer. The liquid crystalline behavior of OBZ─COOH/PSTA is studied by polarized optical microscopy and small angle X-ray scattering analysis. The results show that the OBZ─PSTA forms the LC structure during isothermal and non-isothermal curing. The LC structure displays a floral textured nematic phase. The phase formation is induced by an amidation reaction. Due to the grafts of LC PSTA, the thermal conductivity of OBZ─PSTA is 0.296 W m^-1 K^-1 , which is 26% greater than OBZ─COOH. The glass transition temperature (T_g ) of OBZ─PSTA is 241 °C. The 5% (T_d5 ) and 10% weight loss temperatures (T_d10 ) of OBZ─PSTA are 346 and 362 °C, respectively.