Benzoxazine-epoxy thermosets with smectic phase structures for high thermal conductive materials

ABSTRACT

To further increase the intrinsic thermal conductivity (TC) of polybenzoxazine, a series of benzoxazine-epoxy thermosets (s-PBEI) were obtained through the sequential curing of a smectic phase epoxy monomer (s-EP) and a bifunctional benzoxazine monomer (BZ) in the presence of imidazole. The results show that s-PBEI exhibits a smectic mesophase. The formation mechanism of the smectic phase is reaction-induced phase separation caused by the preferential curing of s-EP. Owing to the increment of the liquid crystalline structure content, the TC of s-PBEI increases with increasing s-EP content. The TC of s-PBEI55 containing equal weight of BZ and s-EP reaches 0.30 W m⁻¹ K⁻¹, which is higher than that of n-PBEI55, a benzoxazine-epoxy thermoset with nematic phase structures. Additionally, the TC, glass transition temperature, and 10% weight loss temperature of s-PBEI64 containing 60 wt% BZ and 40 wt% s-EP are 0.28 W m⁻¹ K⁻¹, 216°C, and 334°C, respectively, indicating its potential applications in electronic packaging, LED lighting, and other fields requiring a high TC resin matrix.

Graphical abstract

A benzoxazine-epoxy thermoset exhibiting smectic phase structures is obtained by sequential curing of a smectic phase epoxy monomer (s-EP) and a bifunctional benzoxazine monomer (BZ) in the presence of imidazole. The thermoset is composed of s-PEI and PBZ cross-linked networks. Compared to the thermoset with nematic phase structures, the corresponding thermoset with smectic phase structures has higher thermal conductivity.

KEYWORDS:

• Benzoxazine
• liquid crystalline epoxy
• smectic phase
• thermoset
• thermal conductivity

Disclosure statement

The authors declare no conflict of interest.

Additional information

Funding

This work was financially supported by Shandong Provincial Natural Science Foundation, China under Grant [ZR2018MB022], Key Research and Development Plan of Shandong Province, China under Grant [2017GGX20141], and Jinan City Science and Technology Startup Enterprise Support Plan, China under Grant [201602102].