Preparation and properties of ternary copolyimide films
Using 4,4'-diaminodiphenyl methane(DDM),4,4'-diaminodiphenyl ether(ODA)and homophenyltetramethylene anhydride(PMDA)as raw materials,by changing the molar ratio of DDM and ODA,ternary copolyimide films containing different DDM contents with 0%,25%,50%and 75%(DDM content is mole fraction of DDM in diamine monomers)were prepared.The comprehensive influences of DDM content on physical and mechanical properties of the polyimide films were investigated.The results show that the imidization of the synthesized polyimide material is completely finished.With the increase of DDM content from 0%to 75%,the temperature at 5%thermal weight loss increases from 357.6℃to 531.2℃.After the introduction of DDM monomer,the transmittance of the polyimide films in the range of visible light(400-800 nm)is more than 85%.In addition,the hydrophobicity of the polyimide films is enhanced due to the introduction of a non-polar group(methylene)in DDM,and the contact angle increases from 66.9°(without DDM)up to 92.1°.The hydrogen bond interaction in polyimide films was enhanced with the introduction of DDM.Under the condition that the third monomer DDM content is 50%,the tensile properties and thermal conduc-tivity of the film are the best,the tensile strength is 192.46 MPa,the elongation at break is 10.23%,the tensile modulus is 3.83 GPa,and the thermal conductivity increases from 0.348 W/(m·K)(without DDM)to 0.399 W/(m·K),which are increased by 48%,42%,56%and 15%respectively compared with those of the polyimide film without DDM.In summary,the ternary copolyimide film has good performance in mechanics,thermal conductivity and transparency,and can be widely used in the field of heat dissipation of electronic components and spacecraft protection.
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