Dynamic Mechanical And Shape Memory Properties Of Copolymers From Benzoxazines Based On Diamines

Three benzoxazines based on o-allylphenol and 1,6-hexamethylenediamine or 4,4?-diaminodiphenylmethane or 4,4?-diaminodiphenyl ether were respectively blended with diglycidyl ether of bisphenol-A?DGEBA?in various weight ratios followed by thermally activated polymerization to prepare three series of benzoxazine/DGEBA copolymers.The copolymerization of benzoxazine/DGEBA was studied by FTIR and DSC.The characteristic changes are the decrease in intensity of the absorption peaks in 918–920 cm^–1 range and at1037 cm^–1 and in 1224–1230 cm^–11 range due to the ring-opening polymerization of oxirane and oxazine rings.For each of the three series of benzoxazine/DGEBA blends,the DSC peak temperature increases with increasing DGEBA content,indicating that the polymerization reaction rate of DGEBA is lower than those of the benzoxazines.The dynamic mechanical properties of the copolymers were studied by dynamic mechanical analysis?DMA?.Inview of the three kinds of benzoxazines,the storage modulus,crosslinking density and glass transition temperature of the copolymers with different components show different variation tendency and the three copolymers show different shape memory properties under bending and tensile deformation modes.In addition,three benzoxazines were synthesized from a set of isomeric fluorophenols?o-,m-,and p-fluorophenols?,4,4?-diaminodiphenyl ether?dde?and formaldehyde.The chemical structures were confirmed by FTIR and NMR.Two series of benzoxazine/PCL-?OH?₂ copolymers were prepared by thermally activated polymerization of the oFP-dde/PCL-?OH?₂ and pFP-dde/PCL-?OH?₂ blends.The curing behaviors were studied by FTIR and DSC.The results show that the peak temperature of the DSC curves of the blends are respectively higher than those of benzoxazines.The dynamic mechanical properties and thermal stabilities of the copolymers were respectively investigated by DMA and TGA.With the increase of PCL-?OH?₂ content,the storage moduli of the two series of copolymers increased first and then decreased,the crosslinking density increased but the glass transition temperature deceased.In tension and bending deformation modes,copolymers with low PCL-?OH?₂ content show higher shape recovery ratios than the pure polybenzoxazines,respectively.However,copolymers with high PCL-?OH?₂ content show lower shape recovery ratios than the pure polybenzoxazines,respectively.TGA results show that the temperatures of 5%weight loss of the copolymers are respectively higher than those of the pure polybenzoxazines.With the increase of temperature,the residues of the copolymers are respectively lower than those of the pure polybenzoxazines at the same temperature.