Dielectric Properties of Bisphenol A Polycarbonate and Its Tethered Nitrile Analogue

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• 作者：John T. Bendler ; David A. Boyles ; Charles A. Edmondson ; Tsvetanka Filipova ; John J. Fontanella ; Mark A. Westgate ; M. C. Wintersgill
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：May 28, 2013
• 年：2013
• 卷：46
• 期：10
• 页码：4024-4033
• 全文大小：456K
• 年卷期：v.46,no.10(May 28, 2013)
• ISSN：1520-5835

文摘

The relative permittivity and dielectric strength have been determined for a bisphenol A polycarbonate (BPA-PC), in which a cyanoethyl group has been substituted for one of the geminal dimethyl groups. The new material (CN-PC) has a glass transition temperature that is 19 K higher than that for BPA-PC. In addition, the dielectric strength of CN-PC, 405 V/渭m, is somewhat smaller than that for BPA-PC, 620 V/渭m. The relative permittivity was determined from 10 to 10⁵ Hz over a wide temperature range and at pressures up to 0.25 GPa. While the real part of the relative permittivity at 10³ Hz and room temperature for BPA-PC is about 3, that for CN-PC is found to be greater than 4. Correspondingly, the 纬 relaxation region in CN-PC is very strong. For the 纬 relaxation, a strong increase in peak height as temperature increases and a strong decrease in peak height as pressure increases are observed. A relaxation is found at temperatures higher than the 纬 relaxation. This process is labeled as the 尾 relaxation because it appears to be related to the 尾 relaxation in BPA-PC in that the strength and position depend on the history of the material. The effects of pressure on the 纬 relaxation for both CN-PC and BPA-PC are quite large and similar to those previously seen for the 纬 relaxation in a fluorinated tetraaryl bisphenol A polycarbonate (DiF p-TABPA-PC). In fact, the activation volume is found to be approximately the same for all three BPA-PC-based materials despite wide variations in both peak position and peak height. Finally, computer studies of the model compounds, 4,4鈥?diphenylpentanenitrile and diphenyl carbonate, were carried out. Both provide insight into the nature of the 纬 relaxation with the latter yielding an activation volume in approximate agreement with the experimental values.