The Influence Of Fluorinated Diamine On Transparent Polyimide Film’s Properties

Polyimide are well known as high performance polymer materials for their excellentthermal stabilities, mechanical, electrical and chemical properties，which have been widelyused in machinery, optoelectronic, automotive, aerospace and so on. Polyimide film was thefirst commercially available materials. When applied as flexible substrates for flexibledisplays and thin film batteries, polyimide film takes the irreplaceable position. Theconventional polyimide films show colors and low transparency because of theintramolecular and intermolecular charge transfer complex (CTC). Two kinds of fluorinateddiamine monomers were developed in this thesis to prepare transparent polyimide films andthe relationship between the physical properties and chemical structure was studied. Fluorinated diamine monomers, in which two benzenes are connected by variousgroups, are applied in this thesis. One type of diamine monomers, containing flexible bridgebonds of ether, thioether or sulfone respectively, were copolymerized with6FDA; And theother diamine monomers, containing rigid structure of biphenyl or terphenyl with shiftedtrifluoromethy and amines substitutes, were applied to prepare the target materials with6FDA as well. All the polyimide were obtained by the standard one-step or two-steppolymerization method. The fourier transformed infrared absorption spectrum(FTIR)、ultraviolet visible light transmittance (UV)、differential scanning calorimetry (DSC) andThermogravimetry Analysis (TGA)was chosen to analyze the chemical structure andphysical property of the polyimide. The conclusions were obtained as the following: (1) The molecular structures of the polyimide were supported by their characteristicpeak in FTIR and high degree of imidization was also confirmed.(2) Polyimide films containing flexible bridge bond of thioether lexhibit the mostflexible backbone and strong intra-molecular CTC among the three monomers, resultingmore absorption in the ultraviolet to ultraviolet-visible regions. Sulfone bridge bond wasmuch more rigid with stronger electron-withdrawing effect, the corresponding filmsexhibited higher transparency. DSC results showed that the flexibility of the backbonesaffected the glass transition temperature and the flexible molecular had a lower Tg. TGAanalysis revealed that all the three materials had good thermal stability.(3) When diamine monomers with stereo-structure containing biphenyl or terphenylwere applied in polyimide toward twisted backbones, the intra-molecular and intermolecularCTC were suppressed in the resulting films and higher transparency was achieved. However,the DSC showed lower Tg obtained due to the weaker intermolecular.(4) The polyimide films obtained in this thesis exhibited transparency about90%withstart point around370nm. And Tg over300℃was also achieved with Td (5%) over450℃.