A comparative study of the polarity and conformational characteristics of diethyl hexafluoroglutarate (DEFG) and its hydrogenated diester counterpart, diethyl glutarate (DEG), is reported. The value at 30°C of the mean-square dipole moment 〈µ 2 〉 of the latter compound, 5.26 D 2 , is nearly 2 times larger the value of this quantity for the fluorinated diester, which amounts to 12.1 D 2 at the same temperature. Values of the conformational energies associated with the rotational states about the skeletal bonds of the acid residue were calculated by combining molecular mechanics with the critical interpretation of the mean-square dipole moment of these compounds, finding that the rotational populations about the different skeletal bonds are similar in both molecules. The evaluation of 〈µ 2 〉 as a function of the conformational energies indicates that the experimental results are reproduced assuming that the conformation in which the C*dO* group eclipses the C R -C bond in the C C R C*(O*)O residue is less stable than the alternative conformation in which the carbonyl group eclipses the C R sF (or C R sH) bond. The analysis suggests that the high polarity exhibited by DEFG, in comparison with that of DEG, arises from differences in the orientation and the modulus of the dipoles in both compounds rather than from differences in their conformational characteristics.

This work reports the transport of carbon dioxide, oxygen, and nitrogen in amorphous membranes of vulcanized natural rubber reinforced with regenerated cellulose. The values of the permeability coefficient of carbon dioxide, oxygen, and nitrogen in the composites with 25% of cellulose, measured at 25 °C and 15 cmHg of pressure, are roughly one‐third of those measured in the same conditions for these gases in natural rubber. The isotherms representing the variation of both the permeability and diffusion coefficients of the gases with pressure present a relatively sharp increase in the region of low pressures, attributed to changes in the free volume. The analysis of the permeability characteristics of the membranes in terms of the free‐volume theory suggests that gas transport is severely hindered in both the cellulose phase and the cellulose–rubber interphase of the composites. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 393–402, 2000

From a comparative study of the polarity of poly(neopentyl glycol hexafluoroglutarate) (PNFG) and its hydrogenated counterpart, poly(neopentyl glycol glutarate) (PNG), the influence of the presence of the fluorine atoms on the conformational characteristics of polyesters is investigated. At 30°C, the experimental values of the mean-square dipole moment per repeating unit of PNG and PNFG chains, 〈µ 2 〉/x, are 5.25 and 9.16 D 2 , respectively. A critical interpretation of the experimental results using the rotational isomeric state model suggests that the conformational energies associated with the gauche states about both the C R H2-C*(O*) and C H2-C R H2 bonds of the acid residue of PNG have, respectively, lower and higher energy than the alternative trans states. Similar conclusions are reached for the conformational energies associated with the skeletal bonds of the C F2-C R F2-C*(O*) segment of the acid residue of PNFG chains. This study leads us to conclude that differences in the orientations of the dipoles associated with the ester groups, rather than differences in the rotational populations about the skeletal bonds of the chains, may be responsible for the significant higher polarity of the fluorinated polyesters.

Temperature-domain analysis of primary and secondary dielectric relaxation phenomena in a nonlinear optical side-chain polymer Thermally stimulated depolarization current investigation of the relaxation behavior of polymers with chlorocyclohexyl side groups Order/disorder phase transitions of liquidcrystalline polymers with rigid groups in the side chains. A lattice theoryThe curves describing the temperature dependence of the dielectric loss for poly(4-acryloxyphenyl)-(4-chlorophenyl)-methanone exhibit a well developed subglass absorption followed in order of increasing temperature by an ostensible glass-rubber relaxation or (Y process. Free charge conductivity processes and blocking electrode phenomena become dominant in the a relaxation at frequencies below 10 Hz. An electric model is proposed to interpret the dielectric results covering the glassy state and the glass-rubber transition. The model is basically a parallel configuration involving a condenser (C,J, a resistance (R), and a Havriliak-Negami-type impedance (Z&J coupled in series with an impedance (Zz) representing the electrode phenomena. The circuit allows one to split the dipolar processes from both free charges and blocking electrode conductivity contributions to the real d and loss C' parts of the complex dielectric permittivity at temperatures above the glass transition temperature of the polymer. At low frequencies the model predicts that d and 6 scale with frequency as E' -u-('+~) and E" -w-', the exponent 5 not being restricted to the conventional value of 0.5 commonly found in the literature.