Studies On Preparation And Properties Of Polyhedral Oligomeric Silsesquioxane/Polyimide Hybrid Films

In inertial confinement fusion physics experiment, the films of around 500 nm which possess excellent mechanical properties at low temperature(< 77K) are needed. This thesis carries out the work of polyimide composite films and their mechanical properties at 77 K because of the lack of commercial films.Since the polyhedral oligomeric silsesquioxane(POSS) was successfully synthesized by chance in the fifties of 20 th, it has attracted a lot of attention as for its unique organic/inorganic hybrid structure and excellent mechanical, thermal, electrical and optical properties. Aromatic polyimides are listed as the most important functional polymer materials in 21 th century because of its outstanding performance. At the same time, it is believed that the properties of hybrid films will be improved effectively by introducing the POSS nanoparticles into the aromatic polyimide substrate.In order to processing the hybrid films, the high accuracy molds with good stability are needed. Therefore, in this thesis, we designed the experimental molds firstly, and then selected a suitable solvent out for the experiment, which was used to solving the POSS nanoparticles. The author of the thesis synthesized two types of hybrid films by sol-gel polymerization technique. At last, the author checked the structure and properties of the hybrid films by Fourier transform infrared reflectance spectroscopy(FT-IR), thermal gravimetric analysis(TGA), scanning electron microscope analysis(SEM) and mechanical analysis at room and low temperature(77K).This thesis mainly contains:First, with the cooperation of other members, we designed the horizontal metal base, clamping frame for imidization of polyimide and mechanical properties test accessories at low temperature.Second, we chose the appropriate solvent to dissolve the POSS nanoparticle, through the experiments, we found that the NMP solvent can dissolve the POSS as well, which provides great convenience for the preparation of polyimide films.Third, this work has prepared hybrid films by sol-gel method through the reaction between the pyromellitic dianhydride(PMDA), p-diaminophenyl ether(ODA). The resulting composite films performance better than the pure PMDA-ODA films, but the thermal stability decreased. By FT-IR, SEM to characterize the structure and morphology of the film section, TG analysis and the mechanical tests at room and low temperature(77K) to study the properties of the films. The optimal results are: when the doping amount of POSS is less than 5wt%, the thermal resistance of the hybrid films remained stable at room temperature and 77 K. The films exhibited superior tensile strength of pure PPI films, especially, when the POSS amount is 3wt%, the tensile strength is 239.38MPa(77K), improved by 17% than the pure PPI, and when the POSS content is 5wt%, the tensile strength is 101MPa(room temperature), improved by 25% than the pure PPI. This is because at low temperature, the polymer chains are frozen, and the particles arranged in PI substrate became closer.Fourth, we prepared the BPI hybrid films by 3,3’,4,4’-biphenyltetra carboxylic dianhydride(BPDA), ODA ether through the sol-gel method. As before, the structure and properties of the BPIs were tested. Compared with the PPI films, the mechanical properties of BPIs were improved obviously. When the POSS amount is 1wt%, the tensile strength is 320MPa(77K), improved by 20.8% than the pure BPI, and when the POSS content is 5wt%, the tensile strength is 281.3MPa(room temperature), improved by 16.7% than the pure BPI.