Preparation And Characterization Of POSS-polyimide Composite Films And Research On Their Atomic Oxygen Erosion Behaviors

With the rapid development of space exploration in China,the number of spacecrafts running in low earth orbit（LEO）is increasing.Under this circumstance,the atomic oxygen（AO）resistant polyimide（PI）films with long-term servicing lives are increasingly required.The current PI films cannot be used in LEO AO environment for a long time.In the current work,the preparation,characterization,and AO erosion behaviors of a series of polyhedral oligomeric silsesquioxane（POSS）modified PI films were carried out in order to meet the increasing requirements of long-term serviceable AO resistant PI films for LEO spacecrafts.Meanwhile,the industrial preparation of corresponding PI/POSS composite films were performed.First,the POSS additives were evaluated and the trisilanolphenyl POSS（TSP-POSS）additive with both of the good thermal stability and good solubility in good solvents for PIs was selected as the AO modifier for PI matrix films.A series of TSP-POSS modified PI composite films（PI/TSP-POSS）have been prepared via the physically blending of the standard poly（pyromellitic-co-4,4’-oxydianiline）（PMDA-ODA）matrix and TSP-POSS additives.The measurement results indicated that the incorporation of TSP-POSS significantly enhanced the AO resistance of the composite films.The atomic oxygen erosion yield（Ey）of the composite films decreased with the increase of the TSP-POSS content.The PI-25 composite film with a 25 wt% loading of TSP-POSS in the PI matrix exhibited an Ey value of 0.22×10^-24cm³/atom after an AO attack of 4.02×10²⁰ atoms/cm²,which is about 7.3 % of the standard Kapton film.Secondly,a series of TSP-POSS modified transparent PI composite films（6FPI/TSP-POSS）have been prepared from the fluoro-containing PI matrix,poly（hexafluoroisopropylidene diphthalic acid dianhydride-co-2,2-bis[4-（4-aminophenoxy）phenyl]hexafluoropropane）（6FDA-BDAF）and TSP-POSS additive.The measurement results showed that the incorporation of TSP-POSS enhances the AO-resistant performance of the composite films while maintaining the intrinsic good transparency of the PI films.The 6FPI-25 composite film with a 25 wt% loading of TSP-POSS showed an optical transmittance of 84.7 % at the wavelength of 450 nm.And the 6FPI-25 film exhibited an AO erosion yield of 0.40×10^-24 cm³/atom after an AO attack of 4.02×10²⁰ atoms/cm²,which is about 13.3 % of the standard Kapton film.Thirdly,a series of TSP-POSS modified PI composite films（FPI/TSP-POSS）have been prepared from the the intrinsically AO-resistant phosphorous-containing PI（FPI）matrix,poly（hexafluoroisopropylidene diphthalic acid dianhydride-co-2,5-bis[（4-aminophenoxy）phenyl]diphenylphosphine oxide）（6FDA-BADPO）and TSP-POSS additive.The measurement results showed that the incorporation of TSP-POSS further enhanced the AO resistance of the composite films.The FPI-25 composite film with a 25 wt % loading of TSP-POSS in the FPI matrix exhibited an AO erosion yield of 0.31×10^-25 cm³/atom after an AO attack of 4.0×10²⁰ atoms/cm²,which is only 1.0% that of the standard Kapton film.At last,on the basis of the above research,the industrial continuous preparation research of PI-POSS composite film（PI-20）was carried out.The PI-20 composite film with a width of 1000 mm was successfully prepared.The measurement results indicated that the film showed excellent AO resistance and good thermal stability and mechanical properties.