Properties Of Copolymers Of Diglycolamine-based Benzoxazines

Three mono-functional benzoxazines were synthesized from three para-substituted phenols(hoxyphenol,p-fluorophenol and p-cyanophenol),diglycolamine(DGA)and formaldehyde solution via solution method.Then,mono-functional benzoxazines were coupled into bi-functional benzoxazines with hexamethylene isocyanate(HDI),espectively.The molecular structures of the benzoxazines were confirmed by ¹H and ¹³C nuclear magnetic resonance(NMR)and Fourier transform infrared spectroscopy(FTIR).The thermal polymerization behavior of the benzoxazines was studied by FTIR and differential scanning calorimetry(DSC).The dynamic mechanical properties and thermal stability of polybenzoxazine were studied by dynamic mechanical analysis(DMA)and thermogravimetric analysis(TG).The results show that the mono-functional benzoxazines can?t polymerized into high molecular polymers.The glass transition temperature(T_g)and the thermal stability of the bi-functional polybenzoxazine based on p-methoxyphenol is higher than that of the p-fluorophenol counterpart.The nature of substituents affects the polymerization behavior of the benzoxazines and mechanical properties and thermal stability of the polybenzoxazines.The mono-and bi-functional benzoxazines were blended respectively with epoxy resin and diamino diphenylmethane(DGEBA-DDM),and two bi-functional benzoxazines(bisphenol A/aniline(BA-a)and o-Allylphenol/diamino diphenylmethane(o AP-ddm)),and these blends were polymerized into copolymers,respectively.Meanwhile,blends and copolymers of phenol/DGA benzoxazine(P-dga)with epoxy,BA-a and o AP-ddm were prepared,respectively.The thermal polymerization behavior of the blends was studied by FTIR and DSC,and the dynamic mechanical properties and thermal stability of the copolymers were studied by DMA and TG.The results show that the initial curing temperatures of the blends are higher than DGEBA-DDM.Compared with DGEBA-DDM polymers,the crosslinking densities of the epoxy-benzoxazine copolymers are lower,and the T_gs and thermal stability are higher.Moreover,the copolymers show good shape memory effect in bending mode.The initial curing temperatures and peak temperatures of the mono-and/or bi-functional benzoxaine blends are lower than those of BA-a and o AP-ddm,respectively.The T_gs and crosslinking densities of the copolymers are higher than those of BA-a and o AP-ddm polymers,but the 5%weight loss of the former are lower than those of the latter.The T_gs and the thermal stability of the copolymers based on para-substituted phenol type benzoxazines are higher than those of the counterparts based on phenol type benzoxazine.