Yung-Chung Chen

Orderly Arranged NLO Materials Based on Chromophore-Containing Dendrons on Exfoliated Layered Templates

Three chromophore-containing dendrons were intercalated into montmorillonite layered silicates via an ion-exchange process. Enlarged d spacings ranging from 50 to 126 A were achieved for these novel organoclays. After the organoclays were blended with a polyimide, the steric bulkiness of the dendrons and the interaction between dendron and polyimide resulted in an ordered morphology. The orderly arranged nanocomposites were characterized by a UV-visible spectrophotometer, a variable-temperature infrared spectrometer, and electro-optical modulation. The dendrons in layered silicates were capable of undergoing a critical conformational change into an ordered structure, indicated by the drastic changes of interlayer distances at certain packing densities. Electro-optical coefficients increased sharply from 0 to 6 pm/V while the conformational change occurred. Furthermore, the addition of a polyimide capable of interaction-induced orientation was found to exert an enhancing effect on the degree of the noncentrosymmetric alignment.

Orderly arranged NLO materials on exfoliated layered templates based on dendrons with alternating moieties at the periphery

Nonlinear optical dendrons with alternating terminal groups of the stearyl group (C18) and chromophore were prepared through a convergent approach. These chromophore-containing dendrons were used as the intercalating agents for montmorillonite via an ion-exchange process. An orderly exfoliated morphology is obtained by mixing the dendritic structure intercalated layered silicates with a polyimide. As a result, optical nonlinearity, i.e. the Pockels effect was observed for these nanocomposites without resorting to the poling process. EO coefficients of 9–22 pm V−1 were achieved despite that relatively low NLO densities were present in the nanocomposites, particularly for the samples comprising the dendrons with alternating moieties. In addition, the hedging effects of the stearyl group on the self-alignment behavior, electro-optical (EO) coefficient and temporal stability of the dendron-intercalated montmorillonite/polyimide nanocomposites were also investigated.

Poly(urethane/malonamide) dendritic structures featuring blocked/deblocked isocyanate units

We have used 4-isocyanato-4′-(3,3-dimethyl-2,4-dioxoazetidino)diphenylmethane and diethylenetriamine as building blocks to synthesize novel poly(urethane/malonamide) dendrons possessing terminal methyl ethyl ketoxime (MEKO) units (blocked isocyanate groups). Heating the MEKO-containing dendrons regenerated the terminal isocyanate groups. Subsequently, the regenerated isocyanate groups would react with any compound with active hydrogens. In one example, the dendrons with the deblocked isocyanates further reacted with stearyl alcohol (C18-OH) to form the corresponding dendrons presenting C18 moieties. This deblocking strategy allows replacement of reactive exterior groups with desired functionality for the construction of dendritic macromolecules.