Studies on the mesophase formation mechanism of polybenzoxazines: polymerisation induction

ABSTRACT

To study the mesophase formation mechanism of polybenzoxazine, a novel linear benzoxazine oligomer bearing cholesteryl side groups [poly(PC-AC)] was designed and synthesised through thermally activated ring-opening polymerisation of a monofunctional benzoxazine monomer (PC-AC). The PC-AC was obtained by Mannich condensation reaction using mesomorphic amine of cholesteryl 4-aminobenzoate, p-cresol and paraformaldehyde as starting materials. During the isothermal polymerisation of PC-AC monomer, the phase evolution from a crystal phase to an isotropic molten phase and then to a liquid crystal (LC) phase was observed. Since it is PC-AC oligomers that form the LC phase, ‘polymerisation-induced LC’ mechanism is put forward. We believe that the structure factors including the confined formation of intramolecular hydrogen bonding and the side chain position of mesogenic units also play an important role in the formation of the LC phase. Furthermore, poly(PC-AC) exhibits a smectic mesophase. This work provides new insight into the LC phase formation mechanism of polybenzoxazines. This is very helpful to guide the rational design and synthesis of polymers with high thermal conductivity and high-temperature resistance.

Graphical abstract

A new concept of polymerisation-induced LC is proposed to describe the mesophase formation of a linear benzoxazine oligomer.

KEYWORDS:

• Liquid crystal polybenzoxazine
• smectic phase
• formation mechanism
• polymerisation induction

Disclosure statement

No potential conflict of interest was reported by the authors.

Supporting information

FTIR spectrum and ESI MS spectrum of PC-AC monomer, GPC chromatogram and FTIR spectrum of PC-AC-245-RT, SAXS profile of PC-AC monomer at 190°C upon cooling, POM image of poly(PC-AC) at 165°C upon cooling and TGA thermogram of poly(PC-AC).

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

The authors are grateful for the financial support from Key Research and Development Plan of Shandong Province, China (2017GGX20141); Shandong Provincial Natural Science Foundation, China (ZR2018MB022); and Jinan City Science and Technology Startup Enterprise Support Plan, China (201602102).