Reaction-induced liquid crystalline polybenzoxazine thermosets containing rosin amine grafts

The novel liquid crystal polybenzoxazine thermosets were synthesized using rosin amine and 4,4′-bis(4-hydroxyphenyl) valeric acid based benzoxazine as biobased raw materials. Firstly, benzoxazine monomer of BZA was synthesized via Mannich reaction of 4,4′-bis(4-hydroxyphenyl) valeric acid, aniline and paraformaldehyde. The BZA further reacted with rosin-derived dehydroabietyl amine to yield benzoxazine containing rosin amine graft (BZR). The ring-opening polymerisation of BZR was carried out by sequential heating at different temperatures. The liquid crystalline behaviour of BZR was studied by POM, DSC and SAXS. The cured polymer of PBZR exhibits smectic structure. The liquid crystal mesophase formation was induced by the ring-opening polymerisation reaction. Due to the liquid crystalline structure, the thermal conductivity (TC) of cured resin of PBZR is 0.289 W/m K, which is 36% higher than that of BZA. The glass transition temperature (Tg) of PBZR is 170°C. Additionally, the 5% weight loss temperature (Td5) and 10% weight loss temperature (Td10) of PBZR are 301°C and 311°C, respectively.