Reaction-induced liquid crystalline polybenzoxazine thermosets using aryl ester bonds as cross-linkages.

The increasing tendency to develop integration in electronic devices lead to the demand for thermally conductive polymeric materials. We offered a simple synthetic route to thermally conductive polybenzoxazine thermosets bearing liquid crystalline structures without the addition of any filler. Benzoxazine monomer of BZ-COOH was synthesized via Mannich reaction of p-hydroxy benzoic acid, p-formaldehyde, and dodecyl amine. After ring-opening polymerization of BZ-COOH, the obtained benzoxazine oligomer of OBZ-COOH was converted into acetoxy-bearing benzoxazine oligomer of OBZ-AC. Through self-crosslinking reaction of acetoxy group and carboxyl group in OBZ-AC using Zn(CH3COO)2 as a catalyst, the polybenzoxazine thermosets of OBZ-PES were produced. The liquid crystalline behavior of OBZ-AC was studied by POM, SAXS, and DSC. The results show that OBZ-AC formed the LC mesophase during isothermal and non-isothermal curing. The LC mesophase displays a layered arrangement of the smectic C phase. The formation mechanism is esterification reaction-induced. Owing to the formation of liquid crystalline structure, the TC of OBZ-PES is found to be 0.284 W/m. K, which is 21% and 16% greater than those of OBZ-COOH and OBZ-AC, respectively. In addition, the OBZ-PES shows excellent thermal performance. Its Tg(G") is up to 269°C. Its 5% weight loss temperature (Td5) and 10% weight loss temperature (Td10) are 383°C and 410°C, respectively. [ABSTRACT FROM AUTHOR]