Synthesis And Characterization Of Siloxane-containing Polyimide And Its Application In Screen Printing

The polyimide adhesive films are widely used in aerospace,microelectronics and others industrial due to the excellent heat resistance,strong mechanical properties,and adhesion property.The siloxane modified polyimides can obviously improve its dielectric properties,visible-light transmittance,hydrophobicity,and adhesion to materials.In this paper,the siloxane segment is introduced into the aromatic polyimides backbone,the effect of siloxane segment ratio,synthesis method and solvents on the properties of polyimide film are studied experimentally,and the possibility that using is as the screen printing ink is explored.The polyimide is synthesized with aromatic dianhydride,aromatic diamine and siloxane diamine(the molecular weight is 860 g mol^-1)as diamine by different synthetic methods.The results show that the temperature has a great effect on the final properties of poly（siloxane-imide）:the difference in imidization temperature around 40 ^oC is sufficient to cause a decrease in molecular weight and in others properties of final polymer（PI-1 imidization temperature 195 ^oC,T_g:207 ^oC,PI-5 imidization temperature 145 ^oC,T_g:151 ^oC）.Compared with thermal imidization,the chemical imidization can effectively improve the performances of polymer,because the chemical imidization method can achieve a larger molecular weight and more concentrated molecular weight distribution.The molecular chain structure of block imparts excellent mechanical properties for polymer,while the blending structure imparts adhesive properties and hydrophobicity.A series of poly（siloxane-imide）with different siloxane diamine ratio are prepared.The molecular weight,IR spectrum,UV spectrum,mechanical and thermal properties of the products are characterized.The results show that the introduction of siloxane diamine effectively enhances the solubility,film forming ability,light transmittance in visible light region,hydrophobicity,and the elongation at break of polyimide films（the one synthesized with complete siloxane diamine:1158%,the one synthesized with complete aromatic diamine:1.1%）.Furthermore,the effect of solvents on the performances is explored by synthesizing poly（siloxane-imide）in N,N’–dimethylacetamide（DMAc）,N–methylpyrrolidone（NMP）and blend solvent of butyrolactone with methyl benzoate respectively.The results show that compared with amine solvent,the mixture of butyrolactone with methyl benzoate can effectively increase the molecular weight and heat resistance,meanwhile,the dielectric property and light transmittance of polymer is reduced（light transmittance at 450 nm of films synthesized in blend solvent:74%;synthesized in DMAc:56%and synthesized in NMP:53%）.Finally,the possibility of using poly（siloxane imide）solution as an ink of screen printing is investigated.The results show that printed picture with this ink has a certain image resolution,excellent solvent resistance and water resistance,etc.In short,the siloxane modified polyimide has excellent dielectric properties,adhesion with copper foil and hydrophobicity,which has laid the foundation for its application in the field of electronic packing.