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

ABSTRACT

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 T_g(G”) is up to 269°C. Its 5% weight loss temperature (T_d5) and 10% weight loss temperature (T_d10) are 383°C and 410°C, respectively.

GRAPHICAL ABSTRACT

KEYWORDS:

• Thermosetting polymer
• liquid crystallinity
• thermal conductivity
• esterification reaction

Acknowledgments

We appreciatively acknowledge the financial support from the National Natural Science Foundation of China (51973104), the Technological Development Research Program (2021DJ6402), PetroChina Lanzhou Petrochemical Co., Ltd Shandong University, and Key R&D Plan of Shandong Province (2022CXGC020602).

Disclosure statement

The authors declare no competing financial interest.

CRedit authorship contribution statement

Irum Rafique: Conceptualization; Methodology; Validation; Writing-original draft; Writing-review & editing; Visualization. Yong Li: Writing-review & editing; Jiming Chen: Writing-review & editing; Visualization. Jianjun Yi: Review & editing. Sujuan Zhang: Writing – review & editing. Shahid: Review & editing. Zaijun Lu: Conceptualization; Methodology; Validation; Formal analysis; Writing-review & editing, Supervision; Project administration.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/02678292.2023.2272763.

Additional information

Funding

The work was supported by the Technological Development Research Program [2021DJ6402], PetroChina Lanzhou Petrochemical Co., Ltd Shandong University, and Key R&D Plan of Shandong Province [2022CXGC020602]; the National Natural Science Foundation of China [51973104].