Ring-Opening Polymerization of 1,3-Benzoxazines via Borane Catalyst

Area of Science:

• Polymer Chemistry
• Materials Science

Background:

• 1,3-benzoxazines are a class of thermosetting polymers with promising thermal and mechanical properties.
• Ring opening polymerization (ROP) is a common method for synthesizing polybenzoxazines.
• Elevated polymerization temperatures can limit the application of benzoxazine resins.

Purpose of the Study:

• To investigate the efficacy of tris(pentafluorophenyl)borane as a Lewis acid catalyst for reducing the ROP temperature of 1,3-benzoxazines.
• To evaluate the impact of this catalyst on the curing kinetics and thermal properties of the resulting polybenzoxazines.

Main Methods:

• Dynamic scanning calorimetry (DSC) was used to determine the onset ROP temperatures.
• Fourier-transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance (¹H NMR) spectroscopy were employed to monitor the polymerization process.
• Thermogravimetric analysis (TGA) was utilized to assess the thermal stability and char yield of the polybenzoxazines.

Main Results:

• Tris(pentafluorophenyl)borane decreased the onset ROP temperatures by up to 98 °C for model benzoxazine compounds.
• Catalytic polymerization proceeded rapidly, achieving fast curing as evidenced by FTIR and ¹H NMR.
• The catalyst significantly increased char yields, with a 3 mol % addition augmenting yields by up to 13%.

Conclusions:

• Tris(pentafluorophenyl)borane is an effective catalyst for lowering the ROP temperature of 1,3-benzoxazines.
• The catalyst facilitates rapid curing and enhances the thermal stability, particularly the char yield, of polybenzoxazines.