Polybenzoxazine (PBz) thermosets have emerged as an alternative class to traditional commercial phenolic polymers due to their superior properties obtained at a lower cost.1-2The advantages of PBz include better thermo-physico-mechanical properties, near-zero shrinkage upon polymerization, low water adsorption, high char yield, molecular design flexibility etc.3 Additionally, benzoxazine (Bz) monomers easily undergoes catalyst-free thermally mediated ring-opening polymerization (ROP) empowering industrial viability. Recent advances include incorporation of sustainable feedstock and/or tailoring new structural motifs in monomer4 to tune the properties of PBz and thus affecting suitability to a vast domain of applications.
I will present how the systematic variation of phenyl-substitution at the oxazine ring of monomer is an effective strategy to regulate properties, as shown in Figure 1.5 Formation of monomers is confirmed by 1D and 2D NMR spectroscopy, HRMS and X-ray crystallography. Furthermore, polymerization temperature and thermal stability of monomers and polymers are determined using DSC and TGA. Intramolecular interaction and stereo-electronic effect of phenyl ring seems to play an active role in controlling mass-loss and thus thermal stability during polymerization, as corroborated using TGA-GC-MS, crystal structure analysis and NBO calculation. Mass loss during polymerization is one of the major problem noticed in the first generation un-substituted monomer. With the substitution at the oxazine ring, minimization of such mass-losses occurs substantially and hence appears as an attractive strategy to design new formaldehyde-free monomers to obtain latest 4thgeneration high-performance PBz thermosets.

Stereo-electronic Effect of Phenyl Substituents on Thermal Properties of Oxazine-Ring Substituted Benzoxazine Monomers & Polymers

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27th CRSI National Symposium in Chemistry

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