| Polyimide（PI）,as a high-performance polymer,has excellent high and low temperature resistance,radiation resistance,insulation,and mechanical properties,and is widely used in solar cells,aerospace,flexible displays,chips,and other fields.In this thesis,from the structural aspect,the alicyclic structure was introduced to the PI main chain to improve the traditional PI dark color,and then the aromatic structure was introduced,aiming to synthesize semi-aliphatic polyimide films with both high transparency and good thermal properties,select the films with better overall performance for composite modification,prepare a series of light-colored transparent PI films,and characterize and analyze them.Using a two-step method,bicyclo[2.2.1]heptanedimethanamine（NBDA）,3-Aminomethyl-3,5,5-trimethylcyclohexylamine（IPDA）as diamines were reacted with four aromatic dianhydride monomers 4,4’-（4,4’-isopropylidene-diphenoxy）-bis-（phthalic anhydride）（BPADA）,dianhydride monomer 4,4’-oxydiphthalic anhydride（ODPA）,3,3’,4,4’-biphenyltetracarboxylic acid dianhydride（BPDA）,3,3’,4,4’-benzophenone tetracarboxylic acid dianhydride（BTDA）for binary polymerization reaction to obtain seven kinds of light-colored transparent PI films,and then introduced 2,6-diaminotoluene（2,6-DAT）and 1,3-bis（4′-aminophenoxy）benzene（TPE-R）on the basis of binary polymerization,and the terpolymerization was modified by 1:1 molar ratio between diamines to obtain Seven kinds of terpolymer PI films.It is shown that PI-1-B（prepared by NBDA and ODPA）films have high optical properties with a UV cutoff wavelength(λcutoff)of 356 nm,a UV transmittance at 450 nm(T450nm)of 87%,a predominantly amorphous morphology with weak crystallinity,a glass transition temperature（Tg）of 152.77℃,the initial decomposition temperature（Td）is 501.6℃,the coefficient of thermal expansion（CTE）of 50～100℃is 62.74 ppm℃-1,the tensile strength is 66.03 MPa,and the elongation at break is 5.08%.The optical properties of the ternary copolymer PI films are slightly reduced,and the film morphologies are all dominated by amorphous structures accompanied by weak crystallinity,among which,PI-1-B1,PI-1-C1,PI-1-E1 and PI-1-F1films can still maintain more than 80%of T450nm.The Tgof four PI films of the NBDA series was significantly higher,and the Tgof PI-1-B1 is 83.08℃higher than that of PI-1-B,the residual carbon rate(Rw800)of all seven films was improved,and the coefficient of thermal expansion of 50～100℃is 48.23 ppm℃-1,and the tensile strength was 76.00 MPa.PI-1-B1 and PI-1-F1 with better overall performance were selected,and the films of NBDA series and IPDA series were prepared by changing the ratio of diamine.It is shown that the film（PI-2-B）has better overall performance when the molar ratio of NBDA,2,6-DAT and ODPA are 4:6:10 in the NBDA series,the film morphology is mainly amorphous structure with weak crystallinity,λcutoffis 359 nm,T450nmis 82%,Tgis 238.11℃,Tdis 493.6℃,the coefficient of thermal expansion of 50～200℃is 55.96 ppm℃-1,with good mechanical properties.In the IPDA series,the films are predominantly in amorphous form,accompanied by weak crystallinity,the optical properties of the film are best when the molar ratio of IPDA and TPE-R is 8:2.As the molar ratio of TPE-R increases,the Tggradually decreases and the thermal stability and mechanical properties gradually improve.A series of light-colored transparent PI/Si O2composite films were prepared by compound modification of PI-2-B with KH570-treated modified nano-silica.The study shows that the series of composite films are mainly in amorphous form and have weak crystallinity at the same time.With the increase of doping amount,the agglomeration phenomenon gradually intensifies,the optical and mechanical properties are reduced,and the thermal stability first decreases and then increases;when the doping amount does not exceed 1.5wt%,the Tgof the composite films increases significantly and the thermal expansion coefficient shows an overall trend of decrease. |
