Primary amine-containing benzoxazines 3 and 6 were prepared from an unsymmetrical diamine 1, in which the amine group ortho to diethyl substituents, the hindered amine, is not reactive toward aldehyde at room temperature. Based on 6, three poly(benzoxazine imide) (PBzI) thermosets were prepared by low-temperature polymerization, followed by thermal treatment. Experimental data show that incorporating thermosetting benzoxazine into a polyimide increased the T g , tensile modulus, dimensional stability, flame retardancy, and contact angle without sacrificing too much in thermal stability.

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A bis(4-hydroxybenzylidene)acetone/aniline-based benzoxazine ( BHBA-a ) was prepared from a bisbenzylidene-containing bisphenol, bis(4-hydroxybenzylidene)acetone ( BHBA ), aniline, and paraformaldehyde through Mannich condensation in a cosolvent of toluene/ethanol (2:1, v/v). The structure of BHBA-a was successfully confirmed by Fourier transform infrared and 1 H and 13 C NMR spectra. According to the differential scanning calorimetry (DSC) thermogram of BHBA , an immediate exothermic peak after the melting peak was observed, suggesting that BHBA is thermally active. NMR data of thermally treated BHBA confirm that the immediate exothermic peak after melting of BHBA in the DSC thermogram is resulted from the curing of a double bond. UV and 1 H NMR spectra of BHBA-a show that the bisbenzylideneacetone moiety underwent dimerization through the [2π + 2π] cycloaddition. Therefore, two procedures were applied to cure BHBA-a . The first one was thermal curing of the double bond of bisbenzylideneacetone and oxazine moieties. The second one was photocuring of the bisbenzylideneacetone moiety, followed by thermal curing of the oxazine moiety. The thermal properties of thermosets were evaluated based on these two procedures. Thermosets of BHBA-a exhibit T g as high as 318 °C for curing procedure 1 and 342 °C for curing procedure 2. These values are much higher than that of a traditional bisphenol/aniline-based benzoxazine thermoset. We conclude that the thermal curing of the double bond of bisbenzylideneacetone and photodimerization of bisbenzylideneacetone contributes to the good thermal properties.

A propargyl ether-containing benzoxazine (4) was prepared from a potassium carbonate-catalyzed nucleophilic substitution of propargyl bromide and a phenolic OH-containing benzoxazine (3), which was prepared from 1-(4-hydroxyphenyl)-1-(4-aminophenyl)-1-(6-oxido-6H -dibenz <1,2> oxaphosphorin-6-yl)ethane (1) by a three-step procedure. The curing reactions of (4) were monitored by IR and DSC. A reaction mechanism was proposed based on the observation. Benzoxazines (3) and (4) were applied as epoxy curing agents. The microstructure and the structure-property relationship of the resulting thermosets are discussed. The double-strand structure in (4)-cured epoxy thermosets afforded higher crosslinking density, and led to higher thermal properties. In addition, the (4)-cured epoxy thermosets possess half the amount of highly polar hydroxyl groups than those of the (3)-cured epoxy thermosets, resulting in a lower dielectric constant, dissipation factor, and water absorption.

A main-chain type polybenzoxazine, PBz (1), with pyridinyl moieties was prepared. When the THF dilute solution of PBz (1) was protonated with HCl, a new absorption signal at 458 nm was observed in the UV-vis spectrum. After being excited at 458 nm, a strong emission at 570 nm was observed in the fluorescence spectrum. This result suggests that the pyridinyl-containing PBz (1) can be used as a proton sensor.