Preparation And Properties Of Bisphenol-S/Aniline Based Benzoxazine And Poly(benzoxazine-co-urethane)

A difunctional benzoxazine monomer, 6,6'-bis(3-phenyl-3,4-dihydro-2H-benzo[e][1,3] oxazinyl) sulfone (BS-a), was synthesized via a solution method using bisphenol-S, aniline, and formaldehyde. The chemical structure of the benzoxazine was verified by Fourier transform infrared (FTIR) spectroscopy, 1~H and (13)~C nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and size exclusion chromatography (SEC).The ring-opening polymerization and reaction kinetics of BS-a monomer is studied by FTIR and differential scanning calorimetry (DSC). The FTIR results show that the chemical structure of BS-a monomer changes gradually with the polymerization reaction proceeding. The absorption intensities of C-O-C, C-N-C, and oxazine ring decrease gradually, and some new absorption peaks appear, such as hydroxyl, Schiff base, etc. In addition, comparing the absorption intensity of a selected band with an internatial standard quantitatively, the difference in the changes of various absorptions during polymerization reaction is clearly seen, so are the change rates of different groups of BS-a monomer at the same reaction temperature and in equal time. The results show that the degree of the changes in air for a selected band is lower than that in nitrogen at the same reaction temperature and in equal time. Based on the dynamic polymerization DSC curves, kinetic parameters were evaluated by Kissinger and Ozawa methods, respectively. The isothermal DSC results show that the polymerization reaction of BS-a monomer follows an autocatalytic mechanism. Thermal degradation behavior of polybenzoxazine (PBS-a) based on bisphenol-S/aniline were studied with FTIR, thermogravimetry-mass spectrometry (TG-MS), thermogravimetry (TG), and differential thermal analysis (DTA). The results show that the thermal degradation of PBS-a begins with the detachment of Schiff base, then the scission of aromatic C-S bond, followed by the cleavage of Mannich bridge structure. The scission pathways of the aromatic C-S bond in argon and air are similar, while the degradation pathways of the Mannich bridge structure in both atmospheres are different. The thermal degradation of PBS-a shows two weight loss stages in nitrogen and air, respectively. Thermal degradation kinetic parameters were obtained from TG curves with Flynn–Wall–Ozawa and Coats–Redfern methods. The most probable kinetic mechanism function is a three-dimensional diffusion model in the initial stage in both nitrogen and air.Poly(benzoxazine-co-urethane) was prepared from bisphenol-s/aniline type benzoxazine (BS-a) with urethane prepolymer based on 2,4-toluene diisocyanate (TDI) and polyethylene glycol. The co-polymerization behavior of BS-a with urethane was studied by FTIR and DSC; The morphology, dynamic mechanical properties, and thermal stability of the copolymer were studied by scanning electron microscope (SEM), dynamic mechanical analysis (DMA), and TG. Meanwhile, the water absorption of the copolymer was determined. Simlar to the catalytic effect of the phenolic hydroxyl group, the active amino group in the urethane prepolymer plays the same role in the ring-opening polymerization of BS-a. With the urethane prepolymer content increasing, the peak temperature of the non-isothermal DSC curves slightly reduces, the glass transition temperature (T_g) and toughness of the copolymer increase. But the thermal stability of the copolymer becomes lower and the amount of water absorbed by the copolymer enhances.