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

Abstract

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).