One atom spacers

Scheme 12.60 Synthesis of cyclophanes formed by few four-membered P-containing rings linked by one-atom spacers 162-165...

Imide-terminated telechelics are also synthesized by metathesis depolymerization, and it is found that phthalimide-substituted olefins allow for productive depolymerization when only one methylene spacer separates the nitrogen atom and the olefin (Fig. 8.21). This combination of steric hindrance around the nitrogen lone pair and decreased electron donation from resonance prevents the negative neighboring group effect. However, secondary acyclic amines are unable to produce telechelics through metathesis depolymerization because of unfavorable catalyst-amine interactions. 

Two-photcMi absorptimi and ultiafast dynamics of spin photoexcitations have been used for the characterizatimi of cmijugated polymers containing platinum atoms (Scheme 10.8). These complexes show a record intersystem crossing time of 1 ps (with one phenyl spacer) and 6 ps (with three phenyl spacers). This tunable ultrafast intersystem crossing determines the intensity ratio of the phosphorescence and fluorescence emissimi bands and is potentially useful for apphcatimis for white OLEDs [32]. 

In another relevant class of side-chain NLO polymer, the chromophore unit is attached to the chain as a side pendant without spacers (type n), in such a way that one atom of the chromophore does belong to the polymer chain generally that atom is the N donor of the chromophore (donor embedded polymers). 

The homologous polybibenzoate with a central oxygen atom in the spacer, PDTMB, exhibits a liquid-crystal state at room temperature, owing to its low crystallization rate [15]. This fact is one of the main differences between P7MB and PDTMB, and is reflected on the mechanical properties of both polybibenzoates. The initial... 

Monomers 24 and 25 behave differently when exposed to catalyst 14, shown in Fig. 8.15. Divinyltetramethyldisiloxane 24 is found to be metathesis inactive due to similar steric inhibitions experienced with divinyldimethylsilane. Monomer 25 is synthesized with one additional methylene spacer unit between the silicon atom and the olefin moiety, which then is reacted with Schrock s [Mo] catalyst. Here, metathesis occurs quite readily, exclusively forming a seven-membered cychc molecule (26) instead of polymer. The formation of the cyclic product can be explained by tire Tliorpe-Ingold effect.15... 

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