Preparation And Shape Memory Properties Of Benzoxazines Based On Cresol

Two series of benzoxazine monomers,namely cresol-polyetheramine-based benzoxazines and cresol-APTMDS-based benzoxazines(oC-aptmds,mC-aptmds and pC-aptmds),were synthesized from polyetheramine d400,1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane(APTMDS),cresol isomers(o-cresol,p-cresol and m-cresol)and formaldehyde vis solution method.The chemical structures of the benzoxazines were confirmed by nuclear magnetic resonance spectroscopy,Fourier transform infrared spectroscopy and elemental analysis.The structural changes of benzoxazines in the polymerization were investigated by Fourier transform infrared spectroscopy,and the thermally activated polymerization behaviors of the benzoxazines were evaluated by differential scanning calorimetry.The results show that the position of the substituents on the benzene ring will lead to different reactivities of the benzoxazine monomers.The dynamic mechanical properties of the resultant polybenzoxazines were determined by dynamic mechanical analysis.The results show that the glass transition temperatures of o-cresol,p-cresol and m-cresol-polyetheramine-based benzoxazines are 13,18 and 75 °C,respectively,and the storage moduli in the glassy state(-40 °C)are 2.50,1.71 and 2.61 GPa,respectively;the glass transition temperatures of poly(oC-aptmds),poly(mC-aptmds),and poly(pC-aptmds)are 68,88 and 123 °C,respectively,and the storage moduli in the glassy state(0 °C)are 1.98,1.78 and 1.81 GPa,respectively.The thermal stability of polybenzoxazines was studied by thermalgravimetric analysis.The thermogravimetric curves show that the char yields are 13%,10% and 20% at 800 °C in nitrogen for o-cresol-,p-cresol-and m-cresol-polyetheramine-based benzoxazines,respectively,and the degradation temperatures corresponding to the 5% weight loss in nitrogen are 241,251 and 239 °C,respectively;and 17%,20% and 34% at 800 °C in nitrogen for poly(oC-aptmds),poly(mC-aptmds)and poly(pC-aptmds),respectively,and the degradation temperatures corresponding to the 5% weight loss in nitrogen are 234,238 and 258 °C,respectively.The two series of polybenzoxazines exhibit one-way dual shape memory behavior in response to changes in temperature around Tg.The polybenzoxazines show excellent shape fixity ratio and shape recovery ratio in bending deformation mode and relatively low shape recovery ratio in tensile deformation mode.Moreover,in tensile deformation mode,the variation in stretching temperature around Tg has no obvious impact on shape fixity ratio,but significantly on shape recovery ratio.