Study on Preparation Methods of Polyimide Films With Low Coefficient of Thermal Expansion
Polyamidic acid solution was obtained by polymerization of three monomers including 4,4'-diamino-2,2'-dimethylbiphenyl(M-Tol),p-phenylenediamine(PDA)and 3,3',4,4'-biphenyltetracarboxylic dianhydride(BPDA)in polar solvent.Polyimide films were prepared by coating and imidization.The performances of the films were characterized by thermo mechanical analyzer and universal testing machine,and effects of polymer composition,copolymer structure,reaction solvent,imidization process and stretching on the coefficient of thermal expansion and mechanical properties of polyimide films were studied.It was found that the stretched polyimide films with block copolymer structure prepared by high boiling reaction solvent and chemical imidization process under the molar ratio of M-Tol,PDA and BPDA of 2∶8∶10 had lower coefficient of thermal expansion and better mechanical properties.
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