The synthesis, chemical characterization and liquid crystalline behavior of a series of seven poly(amidoamine) (PAMAM) codendrimers are described. These compounds were obtained by grafting two types of terminal promesogenic units, that carry either one or two decyloxy chains, in various proportions onto the third generation of PAMAM dendrimer. The average number of promesogenic units was determined by using an original interpretation of the NMR spectra. X-ray diffraction studies show that these compounds exhibit lamellar and/or columnar mesophases. The type of mesophase is determined by the number of each kind of promesogenic units present in a given codendrimer and by the temperature. The evolution of the supramolecular organization of the different molecules is explained as a function of the number of alkoxy chains present around the dendritic core and compared to the models developed for the homodendrimers totally functionalized by promesogenic units with either one or two decyloxy chains.
The preparation of optically active poly(isocyanide)s derived from chiral promesogenic monomers
is reported. Remarkably, the stereogenic carbon atom in the monomer is able to pass its chiral “information”
to the growing polymer backbone which is at least 14 atoms (approximately 16 Å) remote from it. The sense
of helical induction in these conformationally rigid polymers is compared to the helical sense of the cholesteric
phases, as well as to the helical senses of chiral smectic C phases, induced by the monomers in nematic and
smectic C phases, respectively. Both relate to the odd−even rules for chiral sense changes in liquid crystalline
phases. The role of noncovalent interactions in the polymerization has been proven by performing the reactions
at various concentrations and in different solventsthe chiral induction from monomer to polymer is greatest
in most concentrated reactions and in solvents with a balance between high dipolarity−polarizability and low
hydrogen bond accepting and cavitational terms, as determined by an LSER analysis.
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