All-trans oligomers

The compounds (see Scheme 3.1) were monodisperse all-trans oligomers 2,5 -diheptyl-p-divinylbenzene, DHep-OPVn with n = 1-6 being the number of aromatic rings [25], and 2,5-diheptyloxy-p-divinylbenzene DHepO-OPVn with n =... 

Thorn-Csanyi, E., and P. Kraxner. 1997. All trans-oligomers of dialkyl-1,4-phenylenevinylenes— Metathesis preparation and characterization. Macromol Chem Phys 198 3827. 

Cyclic oligomers based on biphospholes are also available via Wittig reactions involving the 5,5 -bis(carboxaldehyde) 53 (Scheme 4.16) [44]. An X-ray diffraction study of 54 revealed that the four P-phenyl groups have an all-trans disposition and that this fully unsaturated macrocycle is distorted [44]. The cavity of the 24-membered heterocycle 54 is rather large, the diagonal distance between two P atoms reaching 6.1 A. 

Figure 12 (a) Optical absorption of trans-PA and a related oligomer. Solid lines polarized absorptions of an oriented PA film (precursor route), calculated from the reflection spectrum (from Ref. 113). The polymer chains are parallel to c. Dashed line absorption of the hexamer all-trans dodecahexaene, in solution in hexane (from Ref. 114). Dotted line hexamer emission in hexane, (b) Optical absorption and reflectivity of unoriented cis- and trans- A films (Shirakawa type) (from Ref. 116). 

All-trans unsaturated ester oligomers have been synthesized by lipase-catalyzed polymerization of diesters of fumaric acid and 1,4-butanediol.217 No isomerization of the double bond was observed, as opposed to the extensive isomerization found during chemical polycondensations. Crystallinity was found in the enzymatically formed unsaturated oligoesters prepared in acetonitrile, whereas industrial unsaturated polyesters are amorphous. 

Champagne, B., Jacquemin, D., Andre, J.-M., Kirtman, B. Ab initio coupled Hartree-Fock investigation of the static first hyperpolarizabihty of model all-trans-polymethineimine oligomers of increasing size. J. Phys. Chem. A 101, 3158-3165 (1997)... 

SEC and high mass fractions were analyzed, the MS peaks due to distinct oligomers did not overlap. All-trans retinoic acid is used when the analyte is an apolar polymer. It gives good results for PS. It gives no signal if the cationization salt (silver salts work best) is not added. Small amounts of soaps and detergents such as sodium dodecyl sulfate have dramatic effects on spectral quality. 

Beside oligomers, a number of structural studies have been performed on polythiophene and its 3-alkylated derivatives, both in their neutral and doped forms, but the determination of the structure of PTs is limited by their inherent low crystallinity [67]. Nevertheless, two stable conformations, a nearly planar all-trans rod and a all-cis heUcal or coil geometries, can be predicted from theoretical calculations for polythiophene [68]. 

Meier et al. have also contributed to the field of cyclic PAV oligomers with the synthesis of cyclic dl -trans (all- ) trimers (e.g. 113) containing alkoxy-substituted 1,7-naphthylene and 1,9-phenanthrylene building blocks, via a Siegrist-type trimerizing olefination [134,135]. Suitable substitution at the periphery of the cyclic trimers allows for the formation of stable, thermotropic discotic mesophases [134]. 

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