A pair of benzoxazine isomers from o-allylphenol and 4,4′-diaminodiphenyl ether: Synthesis, polymerization behavior, and thermal properties

An allyl-containing bifunctional benzoxazine is synthesized from o-allylphenol, 4,4′-diaminodiphenyl ether, and formaldehyde, followed by isomerization in the presence of chlorotris(triphenylphosphine)rhodium(I)/triethylsilane catalytic system yielding a propenyl-containing benzoxazine, and the chemical structures of the two isomers are confirmed. In the thermal activated polymerization, both isomers undergo the oxazine ring-opening polymerization and the radical olefin polymerization with the formation of the corresponding polybenzoxazines, but only one exothermic peak is shown on each of their dynamic differential scanning calorimetry (DSC) curves. After isomerization of allyl into propenyl, the onset and maximum polymerization temperatures decrease, but the temperature range covered by the DSC exothermic peak broadens. Consequently, the structures of the resultant polybenzoxazines are different, and some properties are obviously different, for example, the storage modulus decreases, but the glass transition temperature increases, and the thermal stability is slightly enhanced.