Preparation And Properties Of Shape Memory Benzoxazines Based On Polyetheramine

Three difunctional benzoxazines were synthesized from polyetheramine, formaldehyde and three phenols(phenol, o-allylphenol, o-cresol) via solution method. The chemical structures of the three benzoxazines were confirmed by Fourier transform infrared(FTIR) spectroscopy and nuclear magnetic resonance(NMR) spectroscopy.The structure changes of the three difunctional benzoxazines in the polymerization were investigated by FTIR and solid-state 13 C NMR. The FTIR results show that the characteristic absorption peaks of C–N–C?C–O–C of the oxazine ring and the characteristic modes of the benzene ring with an oxazine ring attached decreased gradually and almost disappeared in the polymerization. In addition, comparing the difference in chemical shift between each pair of monomer and polymer in the solid-state 13 C NMR spectra for the characteristic carbons, significant changes are observed in the resonance peaks of the methylene carbons of the oxazine ring. The polymerization behaviors of the three difunctional benzoxazines were evaluated by differential scanning calorimetry(DSC). The results show that the substituent groups decrease the ring-opening polymerization in comparison to the unsubstituted phenol-based benzoxazine. However, the ortho-positions of the benzene ring with respect to the oxygen of oxazine are blocked by the bulkiness of an allyl group has no more significant influence on the polymerization temperature beyond a methyl group. The dynamic mechanical properties of the three polybenzoxazines were studied by dynamic mechanical analysis(DMA). The dynamic mechanical properties of the resultant polybenzoxazines depend on the structure of the starting phenols. The results show that the glass transition temperatures(Tgs) of poly(P-d230), poly(oAP-d230) and poly(oC-d230) are 91, 40 and 60°C, respectively, and the storage moduli at 0°C are 2.16, 2.05 and 1.72 GPa, respectively. The thermal stabilities of three polybenzoxazines were investigated by thermal gravimetric analysis(TGA). The TGA results show that the 5% weight loss temperatures of poly(P-d230), poly(oAP-d230) and poly(oC-d230) are 227, 226 and 222°C, respectively, and the char yields are about 28, 23 and 22% at 800°C in nitrogen, respectively. The polybenzoxazines exhibit one-way shape memory behavior in response to changes in temperature, and the shape memory effects are evaluated by tensile stress-strain and bending tests with a temperature programme based on glass transition temperature. The two polybenzoxazines based on ortho-substituted phenols show excellent shape fixity ratios in tensile stress-strain and bending tests, relatively low shape recovery ratio in tensile stress-strain test, and perfect shape recovery ratio in bending test. Moreover, in tensile stress-strain test, the variation in stretching temperature around Tg has no obvious impact on shape fixity ratio, but significantly on shape recovery ratio.In order to improve the shape memory properties of the polybenzoxazines, benzoxazine/epoxy copolymers were prepared by thermally polymerization of the oAP-d230/DGEBA and oC-d230/DGEBA blends. The curing behaviors of oAP-d230/DGEBA and oC-d230/DGEBA blends were studied by FTIR and DSC. The dynamic mechanical properties and thermal stabilities of the copolymers were investigated by DMA and TGA. In addition, the shape memory effects of the oAP-d230/DGEBA and oC-d230/DGEBA copolymers were evaluated by tensile stress-strain test, the stretching temperatures and the recovering temperatures were set at their Tgs.