Poly polarizable aromatic groups

The influence of the solvent on chiroptical properties of synthetic polymers is dramatically illustrated in the case of poly (propylene oxide). Price and Osgan had already shown, in their first article, that this polymer presents optical activity of opposite sign when dissolved in CHCI3 or in benzene (78). The hypothesis of a conformational transition similar to the helix-coil transition of polypeptides was rejected because the optical activity varies linearly with the content of the two components in the mixture of solvents. Chiellini observed that the ORD curves in several solvents show a maximum around 235 nm, which should not be attributed to a Cotton effect and which was interpreted by a two-term Drude equation. He emphasized the influence of solvation on the position of the conformational equilibrium (383). In turn, Furakawa, as the result of an investigation in 35 different solvents, focused on the polarizability change of methyl and methylene groups in the polymer due to the formation of a contact complex with aromatic solvents (384). 

Induction forces. These arise when a molecule with a permanent dipole caused by a polar group (C-Cl, C=0, C-NO2), induces a dipole in a neighboring molecule. This effect is particularly strong with aromatics because of the high polarizability of the easily displaced -electrons-e.g., low molecular weight esters and polystyrene, or benzene and poly (vinyl acetate). 

Abkowitz and Stolka (1990, 1991) compared hole mobilities of poly-silylanes and polygermylenes containing aliphatic pendants with compounds that contain only aromatic side groups. While transport occurred via states associated with the backbone chain in both compounds, the nature of the side groups was shown to influence the temperature dependence of the mobility. The results were described by a small-polaron argument, based on the assumption that the polarizability increases when an aromatic pendant group was substituted... 

Compounds, such as those containing the aromatic nucleus and thus tt electrons, are polarizable. When such molecules are in close proximity to a molecule with a permanent dipole, the electric field from the dipole induces a counterdipole in the polarizable molecule. This induced dipole acts in the same manner as a permanent dipole and, thus, polar interactions occur between the molecules. Induced-dipole interactions are, as with polar interactions, always accompanied by dispersive interactions. Aromatic hydrocarbons can be retained and separated in GC purely by dispersive interactions when using a hydrocarbon stationary phase or they can be retained and separated by combined induced-polar and dispersive interactions using a poly(ethylene glycol) stationary phase. Molecules can possess different types of polarity, phenyl ethanol, for example, will possess both a permanent dipole as a result of the hydroxyl group and also be polarizable due to the... 

Abstract The optical inversion of poly(propylene oxide) by solvent is not due to a helix-coil transition or any other conformational change. The inversion was observed also in the monomer or the ether of propylene glycol. The variation of rotivity of solvent seems to be caused by change of the polarizability of methyl or methylene group of polypropylene oxide due to the formation of a contact complex with aromatic solvent. 

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