Research On Synthesis And Properties Of Novel Benzoxazine

By taking advantage of the molecular design flexibility of benzoxazine chemistry, polybenzoxazines with low viscosity and good thermal performance have been synthesized through altering the functional groups and blending. In this thesis, polyether-based benzoxazine precursors (poly(pa-eda)) have been synthesized from the Mannich reaction of paraformaldehyde, phenol and amine-teminated polyether diamines with molecular weight of 230,400 and 2000. The structure of the polymers has been confirmed by proton nuclear magnetic resonance spectroscopy (1H-NMR), Fourier transform infrared spectroscopy (FTIR) and elemental analysis. The curing behaviors of the polybenzoxazines were studied using differential scanning calorimetry (DSC), which indicated a single exothermic curing peak at 240℃for poly(pa-eda2000).The three polyether-based benzoxazine precursors were mixed with traditional single and difunctional benzoxazine (PAF,BAF) in the different ratio. The rotational rheometer, dynamic thermal analysis (DMA) and thermogravimetric analysis (TGA) were used to study on the properties of mixtures of poly(pa-eda)s and PAF, BAR The results show that the melting viscosity of the benzoxazine mixture is kept 0.01 Pas at 150℃for 1h. It imply that benzoxazine mixture is of good flowability for processing. The cured poly(pa-eda2000)-based benzoxazine have the best thermal performance. Its weight-loss temperature at 5% and 10% are 338℃and 370℃, resppectively. The ultimate char yield is up to 64% at 800℃under N2. The dielectric properties of cured resin was performed on broadband dielectric spectrometer, and the results showed they could be used as a good insulator.The cure kinetics of pure benzoxazine and benzoxazine mixtures were studied by utilizing the non-isothermal Differential Scanning Calorimeter at different heating rate. Their kinetic parameters are obtained using Kissinger methods and Grane formula. The rate equation and apparent activation energy of benzoxazines during curing reaction were obtained.A series of benzoxazines containing allyl groups have been prepared using paraformaldehyde, phenol and different toluidine including o-toluidine, m-toluidine, p-toluidine. Their chemical structures were identified by FTIR,1H-NMR. Their DSC results exhibit a single exothermic curing peak at more than 250℃. Mix them with single functional benzoxazine (PAF) was utilized to mix with these allylated benzoxazines to decrease their curing temperature. The thermal properties of obtained polybenzoxazines were evaluated by DMA and TGA. The results indicate that polybenzoxazines obtained from m-toluidine has the best thermal performance. The weight-loss temperature of 5% and 10% are 280℃and 344℃, respectively. The ultimate char yield is up to 34% at 800℃under N2. The bending strength of cured polybenzoxazine based on m-toluidine is higher.