Synthesis, characterization, and thermal properties of benzoxazine monomers containing allyl groups

The polymerization mechanism of allyl-functional benzoxazine (Bz) monomers is reported in this article. Following the traditional route of Bz synthesis, a series of monofunctional Bz monomers were synthesized via allylamine and amine condensation reaction with 2,2-diallyl bisphenol-A and paraformaldehyde. Resulting chemical structures of the synthesized monomers were confirmed by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance analyses. The polymerization behavior of the prepared allyl-functional monomers was studied using differential scanning calorimetry and FTIR. Three reactions were observed in the curing process: polymerization reaction of N-allyl groups in the oxazine ring, ring-opening polymerization of Bz, and polymerization reaction of allyl groups in benzene. Compared to a typical polybenzoxazine (PBz), higher cross-linking density in PBz-allyl-2 leads to a higher glass transition temperature and 5% weight loss temperature, which indicates improved thermal stability in PBz-allyl-2 as well as superior thermal conductivity compared to 2,2-bis(3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl)propane. Data on dielectric properties also show that PBz-allyl-2 outperforms typical PBzs. This work focuses on the manipulation of Bz monomer structures to alter their ring-opening polymerization mechanism, as well as cross-linking, in order to derive a PBz with improved properties.