Terpolymers of vinylidene fluoride (VDF), trifluoroethylene (TrFE), and chlorotrifluoroethylene (CTFE) were synthesized as potential materials for electromechanical transduction. These terpolymers had relatively high molecular weights (∼30 kg/mol) and CTFE levels in the range of 5−10 mol %. The presence of the bulky CTFE units disrupts the sequence length of the crystal, which lowers both the melting and Curie transitions; however, the degree of crystallinity remains high. The formation of smaller, more mobile polar domains gives rise to good electromechanical response. At low electric fields (7 MV/m), longitudinal strains as high as 0.5% are attained. This is significantly higher than the strains achieved with the same terpolymer obtained by bulk polymerization. The present materials exhibit a low mechanical modulus (ca. 0.2 GPa) relative to other VDF−TrFE copolymers. This might limit their use, depending on the application.

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An electrostatic model introduced earlier for predicting the heats of formation and dipole moments of fluorinated and chlorinated methanes is extended with success to longer straight-chain saturated compounds. The results are compared with the group and trigonal additivity approaches and shown to be an improvement in many cases. Discussion of the incremental methylene contribution to the heat of formation is presented for fluorinated and chlorinated species.

Evaluating a material's suitability for an application includes determination of its expected service lifetime. For alternative fuels, this entails assessing, inter alia, their effect on the durability of polymeric engine components, e.g., seals, gaskets, and O-rings. When this is governed by thermally activated chemical deterioration, the conventional approach to characterizing aging is laboratory measurements of property changes of the polymer subjected to accelerated conditions (usually higher temperatures), with the data analyzed by an Arrhenius analysis. However, this method is inefficient and time-consuming when the number of candidate alternative fuels is large. Herein, we test the hypothesis that the activation energy governing thermal oxidation of elastomeric engine components is independent of the fuel; thus, while the aging rate may vary, the effect of temperature is independent of the contacting liquid. Accelerated testing of the thermal oxidation of nitrile rubber O-rings were carried out in three liquids, including a fossil fuel and a bio-fuel. The activation energy obtained from changes in crosslink density, 5 82 kJ/mol, was the same for all liquids and consistent with the broad range of literature values for similar compounds aged in air. This result suggests the possibility that estimates of the lifetime of polymeric engine components require only a single accelerated aging test, with the known activation energy used to predict the durability at the service temperature. This would represent at least an order of magnitude reduction in testing requirements. The extension of the approach to the general aging of polymers exposed to different environments is obvious. V C 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40296.

Random copolymers of ethylene and propylene are usually miscible with the corresponding unsaturated terpolymer (EPDM). Vulcanization of these blends yields networks in which only the EPDM is cross-linked. Despite chemical modification of the EPDM by its reaction with sulfur, there is no phase-separation evident during curing. The blend exhibits substantially higher strength than the corresponding pure EPDM networks, when compared at equal modulus. Thus, nearly miscible blend networks having a large disparity in component cross-linking can circumvent the usual tradeoff between the stiffness and strength of elastomers. This exemplifies a general route to better mechanical properties via blends having a homogeneous phase morphology and whose components have substantially different cross-link densities.

The formation of a network in PTHF inhibits the crystallization of chain units in proximity to the crosslinks. From melting-point-depression measurements, it is estimated that the suppression in crystallizability extends to as much as 8 chain units away from a network junction. This estimate is consistent with the degree of crystallinity measured in various crosslinked PTHF rubbers. The equilibrium melting point for linear PTHF was determined to be 361°K. Although this is significantly higher than previously reported values, the present result is congruent with the melting temperatures measured for crosslinked PTHF, and its use leads to satisfactory predictions of their melting-point depression. The distribution in the lengths of network chains exerted a trivial influence on thermal crystallization behavior. Although this distribution must in principle influence crystallization behavior in so far as it governs crystallizable sequence lengths, differences between uni- and bi-modal network architectures were moderate under the present experimental conditions.

Heats of formation and dipole moments of chlorofluoromethanes are shown to be accounted for quantitatively with an electrostatic model. Initial point charges are placed at infinite distance, and the atoms are moved to molecular dimensions and allowed to polarize. If the heat of formation of the compound is considered to be composed of bond contributions, electrostatic work, and polarization work, a good fit of the experimental data is obtained. The model shows potential for extension to the halogenated ethanes.

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