To investigate the effect of donor unit length on the thermoelectric properties of D-A conjugated polymer,three D-A conjugated polymers(PDPP-DTP,PDPP-2DTP,PDPP-3DTP) based on dithieno[3,2-b:2′,3′-d]pyrrole (DTP) with different donor unit lengths were designed and synthesized.The influence of donor unit lengths on the energy levels of the polymers was studied by electrochemical characterization and density functional theory calculations.With ferric chloride as dopant,the polymer films were oxidation doped.Their optical and thermoelectric properties as well as the temperature dependent resistance were discussed.The results show that the HOMO energy levels of the polymers gradually increase with the extension of the length of the DTP-like donor unit,which makes them easier to be oxidatively doped.At the same dopant concentration,the doped polymers exhibit higher conductivity with the extension of the donor unit length.Among them,PDPP-3DTP shows the highest electrical conductivity of 302.3 S/cm,which is much higher than that of PDPP-2DTP(106.2 S/cm) and PDPP-DTP(64.7 S/cm).The charge transport energy barrier of the polymer films gradually decreases with the extension of the length of the donor unit,which is beneficial for the enhancement of electrical conductivity of doped films.However,the Seebeck coefficient of the doped polymer film decreases with the extension of the length of the donor unit,and the final polymer PDPP-2DTP is doped and optimized to have the highest thermoelectric power factor of 19.4 μW/(m·K²).

The intrinsic flame retardant mechanism of bio?based epoxy resin containing pyridazinone structure was explored through resin ablation experiment, scanning electron microscope,X?ray photoelectron spectrometer,thermogravimetry?infrared simultaneous thermal analyzer,and other characterization methods.The results show that compared with the most commonly used petroleum?based bisphenol A epoxy resin, the resultant bio?based epoxy resin is more likely to form a large amount of intumescent carbon layer structure during combustion and release a large amount of non?combustible gases such as CO₂ and NH₃ with less combustible gases.The intrinsic flame retardant bio?based epoxy resin containing pyridazinone structure exhibits a condensed phase?gas phase synergistic flame retardant mechanism. This study provides new ideas for constructing high?performance intrinsic flame retardant epoxy resin.