Ethynylene-linked multifunctional benzoxazines: the effect of the ethynylene group and packing on thermal behavior

Benzoxazine is a promising next-generation thermosetting resin featuring catalyst-free curing, high thermal stability, and low volume shrinkage upon curing. Mono-, di- and tri-functional benzoxazines, 3(4-( phenylethynyl)phenyl)-3,4-dihydro-2H-[1,3]benzoxazine (1), 1,4-bis((4-(2H-3(4H)-[1,3]benzoxazinyl) phenyl)ethynyl)benzene (2) and 1,3,5-tris((4-(2H-3(4H)-[1,3]benzoxazinyl)phenyl)ethynyl)benzene (3), were synthesized, and their curing behavior and heat resistance were investigated. Difunctional benzoxazine 2 was cured at a temperature higher than the mono- and trifunctional benzoxazines 1 and 3. The weight of the cured resin, poly(2), obtained from 2, was maintained at a higher temperature than either poly(1) or poly(3), obtained from 1 and 3. This stability is presumably due to the molecular arrangement of poly(2), which is more regulated than that of poly(1) or poly(3), as supported by DFT calculations, XRD and density measurements. The cured resins adsorbed CO2 in the order of poly(1) < poly(2) < poly(3).

Automated summary

Benzoxazine is a promising thermosetting resin with catalyst-free curing, high thermal stability, and low volume shrinkage upon curing. The difunctional benzoxazine showed a higher curing temperature and higher weight maintenance at high temperatures compared to the monofunctional and trifunctional benzoxazines. This stability is likely due to the more regulated molecular arrangement of the difunctional benzoxazine. Additionally, the cured resins showed different CO2 adsorption capacities, with poly(2) having the highest adsorption.