Polyimide organic-inorganic hybrid composites with formed in situ inorganic nanophase: influence of host polyimide chemical structure on molecular dynamic and permeability

To observe how changes in the structure of the host polymer affect the dynamic properties and permeability of polyimide matrices and nanocomposites the three series of hybrid organic-inorganic nanocomposites based on linear, branched or cardo polyimides and tetraethoxysilane (TEOS) were analyzed by EPR method using the stable nitroxyl radical 2,2,6,6,-tetramethylpiperidine-1-oxy (TEMPO) as a paramagnetic probe. The EPR data obtained were compared with the results of measuring the volume fraction of pores φ and dielectric permittivity ε as well as with X-ray structural analysis and optical microscopy. The introduction of an inorganic component in all cases led to a decrease in the segmental mobility of the linear and cardo polyimide-based composites as compared with the pure polyimide, due to partial immobilization of organic macrochains during the formation of inorganic microregions. For composites based on linear polyimide correlations are observed between the permeability values and the volume fraction of pores and the dielectric constant. EPR results agree with small angle X-ray scattering data that demonstrate formation of more heterogeneous structure of nanocomposites based on branched polyimide matrix as compared with linear one. According to optical microscopy the TEOS content, that allows obtaining most uniform distribution of inorganic inhomogeneities in the nanocomposites, depends on chemical structure of polyimide and is 40%, 50%, and 5% for linear, cardo and branched polyimides, respectively.

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