Junchao Huang

Polyimide/POSS nanocomposites: interfacial interaction, thermal properties and mechanical properties

Abstract A series of functional polyhedral oligomer silsesquioxnae (POSS)/polyimide (PI) nanocomposites were prepared using a two-step approach, first, the octa(aminophenyl)silsesquioxane (OAPS)/NMP solution was mixed with polyamic acid (PAA) solution prepared by reacting 4,4′-diaminodiphenylmethane and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride in NMP, and second, the polycondensation solution was treated by thermal imidization. The well-defined ‘hard particles’ (POSS) and the strong covalent bonds between the PI and the ‘hard particles’ lead to a significant improvement in the thermal mechanical properties of the resulting nanocomposites. The glass transition temperature dramatically increases while the coefficient of thermal expansion (CTE) decreases, owing to the significant increase of the cross-linking density in the PI–POSS nanocomposites. The thermal stability and mechanical property of the nanocomposites were also improved.

Thermomechanical properties of polyimide-epoxy nanocomposites from cubic silsesquioxane epoxides

Novel polyimide-epoxy organic–inorganic nanocomposites are prepared by in situ curing of polyamic acid macromolecules with two POSS epoxides, octa[(epoxycyclohexylethyl)dimethylsilyloxy]silsesquioxane (OC) and octa[(epoxyhexyl)dimethylsilyloxy]silsesquioxane (OH). Comparison between two series of nanocomposites from OC and OH provides a typical example of controlling the macro-scale properties by adjusting the nano-tether structure of the POSS molecules. DMA studies conclude that the crosslink densities of the polyimide-epoxy nanocomposites increase significantly; the nanocomposite networks are predominantly formed by the linkage between the terminal amine groups of the polyimide molecules and the epoxide groups of the POSS molecules. Furthermore, it is interesting to observe that although the crosslink densities of nanocomposites increase significantly, the compressive moduli, hardness and coefficients of thermal expansion change only slightly.

Nano-hybrid luminescent dot: synthesis, characterization and optical properties

A series of nano-hybrid light emitting dots with diameter range from 2 nm to 4 nm were synthesized through grafting organic conjugated chains directly onto an inorganic rigid cage polyhedral oligomeric silsesquioxanes (POSS). The effect of chain length, side groups, polarity of solvents on the property of light emitting dots were studied using FTIR, XRD, DSC, UV, PL, AFM and SEM. The unique structure of these nano-hybrid dots renders them with excellent PL properties which are much different from bulk organic molecules or conjugated polymers. The incorporation of conjugated molecules onto POSS transforms the oligo-conjugated arms from crystalline state to non-crystalline solid which can be solution processed. The PLQE (PL quantum efficiency) of the oligo-conjugated arms in condensed state increases significantly after grafting onto POSS. The light emitting dots are very sensitive to the polarity of organic solvents due to their nano-scaled size. PL spectrum of the nano-hybrid dots in solid film was blue shift from that in most of organic solvents.