Preparation And Properties Of Polybenzoxazines Based On Allylphenols

Three series of benzoxazine monomers were synthesized by allyl-containing phenols and different kinds of amines.Two benzoxazines(EU-f-Si and SIE-dga)were synthesized from eugenol,1,1,3,3-tetramethyldisiloxane,furfurylamine and diethylene glcol amine,two benzoxazines(TMD-dga and TMD-3a)were synthesized from o-allylphenol,1,1,3,3-tetramethyldisiloxane,diethylene glycol amine and 3-amino-1-propanol,and four benzoxazines were synthesized from phenol,p-cresol,o-cresol,o-allylphenol and diethylene glycol bis(3-aminopropyl)ether.The chemical structures of the benzoxazines were confirmed by nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy(FTIR).The structural changes of benzoxazines in polymerization and the thermally activated polymerization behaviors of the benzoxazines were evaluated by FTIR and differential scanning calorimetry,respectively.The results show that the position of the substituents on the benzene ring affects the reactivities of the benzoxazine monomers.In view of the position of the substituents on the benzene ring,the ring-opening polymerization temperature decreases in the order of ortho,para and unsubstituted.The dynamic mechanical properties of the resultant polybenzoxazines were evaluated by dynamic mechanical analysis,and the results show that the glass transition temperature increases with the crosslinking density.The thermal stabilities of polybenzoxazines were studied by thermolgravimetry.The thermogravimetric curves show that the char yields are 49.6%and 48.0%at 800°C in nitrogen for poly(EU-f-Si)and poly(SIE-dga),respectively,and the degradation temperatures corresponding to the 5%weight loss in nitrogen are 281 and 293°C,respectively.The char yields are 12%and 26%at800°C in nitrogen for poly(TMD-dga)and poly(TMD-3a),respectively,and the degradation temperatures corresponding to the 5%weight loss in nitrogen are equal(240°C).The char yields are 24%,17%,16%and 22%at 800°C in nitrogen for phenol-,p-cresol-,o-cresol-and o-allylphenol-diethylene glycol bis(3-aminopropyl)ether-based polybenzoxazines,respectively,and the degradation temperatures corresponding to the 5%weight loss in nitrogen are 261,251,248 and 253°C,respectively.For each series of polybenzoxazines,a higher cross-linking density leads to a higher thermal stabilities,and a longer flexible chain results in a lower thermal stabilities.The shape memory effects were measured by tensile and bending tests.The results show that the three series of polybenzoxazines exhibit one-way dual shape memory behavior in response to changes in temperature around T_g,and the shape fixing ratios and shape recovery ratios in bending deformation mode are respectively better than those in tensile deformation mode.