Study On The Synthesis And Thermal Behavior Of Benzoxazine With Maleimide And Allyloxy Groups

Benzoxazine with maleimde and allyloxy groups is synthesized by the reaction of allyloxy compounds, maleimide compounds and peraformaldehyde. The reason to research it is that there are three kinds of reactive functional groups, maleimide, allyloxy and benzoxazine ring in its molecular structure. In practice, it can be used as high-performance resin matrix, as well as a low molecular weight modifier.Firstly, this paper has probed into the synthesis of allyloxy aniline compounds. During the experiment, we have carefully researched the synthetic conditions' influence on the final rate of production. Two ways of synthesizing of 2-allyloxyaniline and 4-allyloxyaniline are given and compared, the aniline protection / deprotection way and the reduction of nitro group from nitro-phenol as initial raw material. The result shows the latter one is better. It is suitable to synthesize 3-allyloxyaniline for the former.Two benzoxazines, compounded with maleimide group, 3-phenyl-3, 4-dihydro-2H-6- (N-maleimido)-1, 3-benzoxazine(MIB), 3-(4-allyloxy)phenyl-3, 4-dihydro-2H-6-(N-maleimido)-1, 3-benzoxazine(AMB), were synthesized from N-(4-hydroxyphenyl) maleimide, paraformaldehyde, aniline and 4-(allyloxy)-benzene amine. Structures of AMB were confirmed by FT-IR and ¹H NMR as well as elemental analysis. MIB and AMB were found to readily soluble in common organic solvents, such as acetone, methanol, chloroform, tetrahydrofuran et al. The only minor difference in structure between them is that AMB has a flexible and thermally reactive allyloxy group in molecular structure. AMB have a melting point of 129.5℃. Using differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) technology, thermal properties of AMB were studied comparing with that of MIB. It was found that, AMB could be cured at relatively lower temperatures (150～200℃). After thermal self-polymerization of AMB at 150℃for 20 min., the product showed a five percent weight temperature(T₅) of 449℃and a char yield of 65% at 800℃respectively, much higher than that ofMIB (T₅: 375℃; char yield: 56% at 800℃). In addition, AMB has three different kinds of curing mechanisms: the Claisen rearrangement reaction of allyoxy, the ene reaction of allyl and maleimide groups and curing reaction of benzoxazine ring. The three exothermic reactions overlap each other. The phenol hydroxy from Claisen rearrangement reaction of allyloxy catalyse the ring opening reaction of benzoxazine.The curing behaviors of AMB have been studied in details by non-isothermal and dynamic differential scanning calorimetry (DSC). Kissinger equation and Freeman-Carroll equation has been introduced to deal with the data of DSC analysis. Freeman-Carroll equation shows that the activation energy and the order of the reaction decrease with the increase of calefactive speed.