Structure-property relationships in polyimide molecular composites

Rigid rod-like polyimide (PIR)/flexible-chain polyimide (PIF) molecular composites, with 20, 40, 50, 60 and 80 wt. % of the rigid component, were prepared and their structure and molecular dynamics were investigated, in relation to those in pure PIR and PIF. SAXS, DSC, DMA, TSDC and laser-interferometric creep rate spectroscopy (CRS) techniques were used for characterization of nanostructure, glass transition and sub-T-g relaxations at temperatures from 100 to 600-650 K. All the experiments indicated pronounced deviations from additivity in both nanostructure and dynamics of molecular composites. Mixing of the PIR and PIF components led in particular to a smaller nanostructure, down to formation of the nano scale-homogeneous composite. Changes of the dynamic characteristics in two opposite directions and arising of large dynamic heterogeneity around T-g were observed as a result of confinement/constraining effects.