RESUMO
A series of m-phenylene ethynylene oligomers containing nonpolar, (S)-3,7-dimethyl-1-octanoxy side chains have been synthesized and studied. In apolar alkane solvents, oligomers of sufficient length (n > 10) were found to adopt a helical conformation with a large twist sense bias. In contrast, in chloroform the oligomers adopt a random coil conformation. Surprisingly, the strong twist sense bias was determined to be highly time dependent and is partially attributed to intermolecular aggregation.
RESUMO
Cooperative interactions among the side chains of the helically folded phenylene-ethynylene oligomer shown (n=2, 4, 6, 8, 10, 12, 14, 16, 18) can induce a twist sense bias. Therefore, the side chains can play more than just an ancillary role in these conformationally ordered oligomers. The onset of the twist sense bias lags significantly behind the appearance of helical conformations, possibly because a large ensemble of "collapsed" conformations is initially formed.
RESUMO
More than 50 years after Otto Bayer's detailed description of [m,n]-polyurethanes, the first general synthesis of [n]-polyurethanes 1 is described. This series of aliphatic [n]-polyurethanes is synthesized by the in situ polymerization of the corresponding alpha,omega-isocyanato alcohol monomers, which in turn are made out of linear alpha,omega-amino alcohols and di-tert-butyltricarbonate. Polymers of high molecular weight possessing a uniform microstructure are obtained, while their melting points show a strong odd-even effect.
