Structure-thermal property interrelationships are characterized and reported for organic/inorganic addition cure polyimide composite matrices based on 3,3',4,4'-benzophenone tetracarboxylic dianhydricle, the reactive terminal group 4-phenylethynyl phthalic anhydride, and stoichiometric controlled diamine ratios of 1,3-phenylenediamine, 1,4-phenylenediamine, or 4,4'-(1,3-phenylenediisopropylidene) bisaniline, combined with bis(p-aminophenoxy) dimethyl silane or an alpha, co-bis(3-aminopropyl) polydimethylsiloxane oligomer. Polymerization of monomer reactants resin solutions, carbon fiber prepregs and composites, and imidized oligomers are characterized to relate molecular chemical structure and morphology to glass transition temperature, processing characteristics, thermodynamic properties, and thermal stability. Glass transition temperature, thermal decomposition temperature, and char yield were found to increase with increasing siloxane block length in the imide backbone. As the concentration of inorganic component in the imide oligomer backbone increased, the cured glass transition temperature decreased. Char yield and thermal decomposition temperature were observed to decrease as the inorganic component concentration increased. Incorporation of bis(p-aminophenoxy) dimethyl silane into the imide oligomer structure did not provide any significant advantages over traditional polyimides relative to thermal properties or composite processing, but aminosiloxanes improved composite toughness, prepreg tack, and composite processability. (c) 2007 Wiley Periodicals, Inc.