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461.
María Lago-Silva María Magdalena Cid Prof. Emilio Quiñoá Prof. Félix Freire 《Angewandte Chemie (International ed. in English)》2023,62(29):e202303329
Helix inversion in chiral dynamic helical polymers is usually achieved by conformational changes at the pendant groups induced through external stimuli. Herein, a different mechanism of helix inversion in poly(phenylacetylene)s (PPAs) is presented, based on the activation/deactivation of supramolecular interactions. We prepared poly[(allenylethynylenephenylene)acetylene]s (PAEPAs) in which the pendant groups are conformationally locked chiral allenes. Therefore, their substituents are placed in specific spatial orientations. As a result, the screw sense of a PAEPA is fixed by the allenyl substituent with the optimal size/distance relationship to the backbone. This helical sense command can be surpassed by supramolecular interactions between another substituent on the allene and appropriate external stimuli, such as amines. So, a helix inversion occurs through a novel axial-to-helical communication mechanism, opening a new scenario for taming the helices of chiral dynamic helical polymers. 相似文献
462.
463.
Marvin Bishop Julian H. R. Clarke Juan J. Freire 《Macromolecular theory and simulations》2000,9(8):550-554
Off‐lattice Monte Carlo simulations employing the pivot algorithm are used to generate ideal and excluded volume linear polymers in three dimensions. The structure function at large wavevectors is calculated from the resulting configurations. This is compared to the exact equation for ideal chains and to experimental data and both scaling and renormalization group predictions for excluded volume chains. It is found that using the des Cloizeaux form for the distance distribution function in an analytic calculation of the structure function leads to close agreement with the experimental and Monte Carlo data. 相似文献
464.
Juan J. Freire Luis A. Molina Antonio Rey Keiichiro Adachi 《Macromolecular theory and simulations》1999,8(4):321-327
A dynamic Monte Carlo algorithm is employed to investigate the dynamics of flexible linear and star chains on a cubic lattice at different concentrations. Some results for similar systems are also obtained with an off‐lattice algorithm. Diffusion coefficient, relaxation times and mean size data are combined into friction‐independent ratios in good agreement with the theoretical predictions from the Rouse theory. The relaxation times and amplitudes corresponding to the Rouse normal modes are analyzed in terms of their variation with the mode order. The end‐to‐end vector correlation times obtained from the simulations for linear chains are compared with the theoretical expression obtained from the Rouse theory. Deviations from this theory are observed for the contribution of the different modes in the non‐dilute systems. Finally, the time correlation function corresponding to a subchain's end‐to‐end vector is investigated. The results also show deviations from the Rouse theory, which are in qualitative agreement with the features observed in data from dielectric relaxation experiments of block copolymers. 相似文献
465.