Preparation And Thermal Character Of The Novel Benzoxazines

Benzoxazines were a new class of thermosets. They have attracted enormous interest inmany research fields in recent years because of their outstanding properties: i) flexibilitymolecular structure; ii) simple curing process; iii) no micromolecure release and the volumeshrinkage approximate to zero upon curing; iv) the curing products with lower voids andwater absorption、higher glass transition temperature (Tg) which even higher than the curingtemperature sometimes, good thermostability and flame restriction; v) excellent mechanicalproperties. Yet the curing products of the benzoxazine resins were brittleness and the curingtemperature of the benzoxazine resins was too high. These imperfections limited theapplication of benzoxazine resins in some field which had special claim of the properties ofthe materials.So in this paper, the six novel benzoxazine compounds have been desighed and prepared,and their curing behavior have been studied. The attempt was improving the class-link densityof the curing products which could enhance their thermal properties.1) In the six novel compounds, BOZ-031, BOZ-037, BOZ-041and BOZ-047were withstrong electrondonating methoxyl group, and BOZ-021and BOZ-027were with either strongelectondonating ether group or weak electrondonating allyl group. The structure of them hadbe assaied by fourier transform infrared spectroscopy(FTIR), hydrogen nuclear magneticresonance(1H-NMR), mass spectra(MS), et al.2)“Water-washing method”“alkaline-washing method” and “setting method”, the threemethods for postprocessing of benzoxazine compounds were investigated, which were used toimprove the purity of the precursors of the benzoxazine resins. The results revealed“alkaline-washing method” and “setting method” were better than “water-washing method”.Using “setting method”, the purity of the BOZ-021increased to99.9%and the single crystalof it was obtained also. Besides, the purity of the BOZ-047was improved observably whichshowed the disappear of the characteristic peak of the dimer and the oligomer of the monomerfrom the1H-NMR spectra of the product.3) The curing behavior and thermal properties of the benzoxazine resins wereinvestigated by differential scanning calorimetry (DSC) and themogravimetric analysis (TGA).The results showed which associated with the purity of the monomer and the position of thesubstituent group on the benzene ring of the benzoxazole ring. i) Oligomer of the monomercould catalyze the ring-opening reaction of the benzoxazine, and also might cause blister upon curing and lead to decrease of the properties of the curing products; ii) weak electrondonatingallyl group at any position of the benzoxazole ring could provide additional polymeric pointto increase the class-link density of resin, then improve the thermostability of the benzoxazineresin; iii) The reactivity was low when the ortho-position and para-position were occupied bysubstituent group and the thermal properties of which were inferior to those with nonesubstituent group or just with a substituent group on the meta-position of the benzene ring; iv)The applicable curing process was100℃/1h—120℃/2h—150℃/2h—180℃/2h—200℃/2h—220℃/1h.4) The investigation of the benzoxazine resin blended with epoxy resin revealed that thecomposite resin could not cure without extrinsic curing agent when the weight percentage ofthe epoxy resin exceed50%. The best ratio of the benzoxazine resin to epoxy resin was7:3and the temperature of5%weightlessness of the blends was325℃; the700℃carbon-residuerate of the blends was24%.