Multistep Continuous Synthesis of a Highly Fluorescent Tröger’s Base-Derived Benzoxazine: Its Thermal Conversion into Intrinsic Microporosity Polymers

Abstract

Troger's base (TB), with its rigid V-shaped geometry, is frequently used as a building block to create polymers with intrinsic microporosity (PIMs). On the other hand, polybenzoxazines have received a lot of attention for a wide range of applications such as high thermal stability, metal ion detection, and cathodic material in batteries. Therefore, in the present work, we describe the first example of Troger's base-derived benzoxazine and its thermal transformation into Troger's base-benzoxazine-derived polymer of intrinsic microporosity. The desired Troger's base-derived benzoxazine is synthesized through a continuous three-step (Schiff base, reduction, and Mannich) approach starting from Troger's base, 2,8-dimethyl-6H,12H-5,11-methanodibenzo[b,f ][1,5]diazocine-3,9-diamine, with no intermediate isolation and purification, and its transformation into Troger's base-benzoxazine-derived PIM is performed through ring-opening polymerization. The continuous threestep synthesis approach for Troger's base-derived benzoxazine and the formation of Troger's base-benzoxazine-derived PIM has never been reported previously. The chemical structure of Troger's base-derived benzoxazine is established using Fourier transform infrared (FTIR), nuclear magnetic resonance spectroscopy, and DFT calculations. The thermal formation and curing behavior of Troger's base-benzoxazine-derived PIM are monitored using FTIR, differential scanning calorimetry, and thermogravimetric analysis. Interestingly, the fluorescence emission of Troger's base-benzoxazine is observed to be significantly pronounced exclusively in a solution state. Conversely, Troger's base-benzoxazine-derived PIM exhibits a notable fluorescence emission solely in the solid state. Furthermore, the emission maximum of the PIM undergoes a red shift when the curing temperature is increased. The present research is expected to result in the development of a thermally stable benzoxazine-derived PIM that can be cured, and its degree of curing can be measured by monitoring the change in the fluorescence color.