Structure-Properties Correlation in Polyimide/Silica Hybrids

Polyimide/silica hybrids were prepared by a sol-gel process and were evaluated in terms of curing behaviour, morphology, water sorption properties and mechanical performances at ambient and at higher temperatures. The spectroscopic examination showed that the presence of the inorganic phase catalyses the imidization reaction of the polyamic acid pre-polymer. Two types of morphology were obtained by tailoring the composition of the precursor solution mixture, i.e. phase-separated or co-continuous systems. Water sorption was found to be strongly influenced by the system morphology. The presence of the inorganic phase increased considerably the amount of absorbed water and phase separated hybrids absorbed more than co-continuous hybrids. Also the mechanical properties were found to depend on the system morphology. The largest increase in rigidity both at ambient and at temperatures up to 250°C was achieved when the two phases were co-continuous.. Conventional two phase systems, on the other hand, exhibited improved fracture toughness.