| With the development of science and technology,optoelectronic devices are gradually becoming more flexible,wearable and bendable,such as OLEDs display substrates,film solar cell substrates,etc.The future development has made the research of flexible optoelectronic devices become the hotspots of concern to researchers.Replacing the conventional glass substrate material with the flexible transparent polymer film is an important method for making the device flexible.Some traditional transparent polymer films cannot meet the post-process temperature requirements due to the low heat-resisting temperature.However,the transparent polyimide(PI)film exhibits excellent performance in terms of transparency and thermal stability,it is expected to meet the application requirements of photovoltaic devices for substrate materials.At present,more and more enterprises such as DuPont,Toray DuPont,Korea Cologne and Taimide have successfully prepared highly transparent PI films by using fluorine-containing monomers.In this experiment,4,4'-diamino-2,2'-bistrifluoromethy biphenyl(TFMB),2,2-Bis(3,4-anhydrodicarboxyphenyl)hexafluoropropane(6FDA)and 3,3',4 4'-biphenyl tetracarboxylic dianhydride(BPDA)were used as the reactive monomer,via solution polycondensation,to prepare a series of copolyimide films by chemical imidization.A series of random copolyimide films were prepared by changing the proportion and feeding method of non-fluorinated monomer BPDA.On this basis,in order to change the arrangement of the molecular segment sequence,firstly,two kinds of oligomers terminated by reactive groups were synthesized.Then the two oligomers were mixed according to a certain proportion,via changing the ratio of non-fluorinated monomer BPDA in dianhydride monomer to prepare a series of multi-block copolyimide film.The properties of the two series of fluorinated copolyimide films were analyzed by testing.The results showed that the feeding mode of non-fluorinated dianhydride monomer BPDA had different effect on the properties of random copolyimide film.The proportion of non-fluorinated monomer BPDA in dianhydride also had different effect on the performance of two kinds of copolyimide films.When the proportion of BPDA was same,the performance of multi-block copolyimide film and random copolyimide film,which were prepared by different copolymerization methods was different.The two kinds of copolymerized fluorine-containing PI films were soluble in the aprotic polar solvent at room temperature,and the film had a high light transmittance in the visible light range.As the content of BPDA increased,the optical properties decreased slightly,and the thermal properties and mechanical properties were improved.When the mole ratio of non-fluorinated dianhydride monomer BPDA accounted for 68.97% of the dianhydride monomer,the transmittance of the random copolyimide film and the multi-block copolyimide film was respectively 91.40% and 91.70% at 500 nm,which were more than 90%.When the mole ratio of non-fluorinated dianhydride monomer BPDA accounted for 35.71% of the dianhydride monomer,the decomposition temperature at 5% weight loss of the random copolyimide film and the multi-block copolyimide film was 563.68°C and 571.54°C respectively.And the tensile strength was 100.98 MPa and 107.31 MPa respectively.When the molar ratio of BPDA monomer is constant,the block copolyimide film had a lower CTE value than the random copolymimide film.And the increase in the proportion of non-fluorinated monomer BPDA coulde greatly reduce the linear thermal expansion coefficient of the two copolyimide films.When the proportion of BPDA was same,the thermal and mechanical properties of multi-block copolyimide film was better than that of random copolyimide film,while the optical properties of multi-block copolyimide film was reduced.At the same time,the change of feeding mode of the non-fluorinated dianhydride monomer BPDA had different effects on the optical properties,mechanical properties and mechanical properties of the random copolyimide film. |
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