Study On Polyimide/Silica Nano-Hybrid Films

Polyimide(PI), as one of the highest comprehensive performance material, exhibits excellent thermal properties, mechaimical strength and dielectric properties. It has been the matrix material for the high performance composite and one of the materials with outstanding heat-resistance. With the developing of the new techonogy in our country, more requirements have been provided on the properties of the PI hybrids. Mechanical, thermal properties and the morphology of the PI hybrids have been studied widely. In this dissertation, the inflences of different couple agents, endcappers and precursors on the aggregation structure of PI/SiO₂ nano hybrid films of were studied.In this paper, the hybrids films of PI/SiO₂ were synthesized via sol-gel route and thermalimidization by the hydrolysis and condensation of tetraethoxysilane (TEOS)and methyl-triethoxysilane (MTEOS), dimethyldiethoxylsilane(DDS) that served as the precursors of the inorganic moiety and produced the silica nano-particles in situ in the polyamic acid solution based on the stepwise poly-condensation of pyromelliticdianhydride(PMDA) and 4,4'oxydianiline(ODA)in N,N′-dimethylacetamide (DMAc). The adopted couple agents are 3-amion-propyltriethoxysilane(APrTEOS),3-glycidoxypropyltrimethoxysilane (GPTMOS), triethoxyvinylsilane (TEVS).The chemical structure was characterized by Fourier Transform Infrared Spectroscope (FT-IR). The aggregation structure of the hybrid films was characterized by Atmoic Force Microscope (AFM) and Scanning Electronic Microscope (SEM), including the fracture and surface morphology.All the results indicated that the inorganic particles in nano size were dispersed when the silica content was 5wt%. When the silica content was 25wt%, the morphology of inorganic phrase transited from small isolated spheric-like granules to IPN structure in PI/TEOS-SiO₂ films.But in PI/MTEOS-SiO₂ films the organic particles from small isotated oval-like ones to big micro-agglomarations.In PI/DDS- SiO₂ films, the silica particles were almost in shape of rod–like and there were many pores in the organic phrase. The results show that the coupling agents can alter the compatibility between the inorganic phrase and the organic one. It didn't reach to the expected result if the coupling agents as only one influcing factor on the aggregation mophologies hybrid films. Other effects must be considered for example silica contents, solid contents and test conditions and so on. Different organic precursors and couple agents could have effect on the aggregation structure of the hybrid films. In this paper the effect of endcappers on PAA molecular and the breakdown strength of the hybrid films were studied. From the data, we can conclude that the breakdown strength of the hybrid films are higher than that of the pure PI film.