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/μm, is somewhat smaller than that for BPA-PC, 620 V/μm. The relative permittivity was determined from 10 to 10 5 Hz over a wide temperature range and at pressures up to 0.25 GPa. While the real part of the relative permittivity at 10 3 Hz and room temperature for BPA-PC is about 3, that for CN-PC is found to be greater than 4. Correspondingly, the γ relaxation region in CN-PC is very strong. For the γ 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 γ relaxation. This process is labeled as the β relaxation because it appears to be related to the β relaxation in BPA-PC in that the strength and position depend on the history of the material. The effects of pressure on the γ relaxation for both CN-PC and BPA-PC are quite large and similar to those previously seen for the γ 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′-diphenylpentanenitrile and diphenyl carbonate, were carried out. Both provide insight into the nature of the γ relaxation with the latter yielding an activation volume in approximate agreement with the experimental values.

The relative permittivity, loss, and breakdown strength are reported for a commercial sample of bisphenol Apolycarbonate (comm-BPA-PC) and a purified sample of the same polymer (rp-BPA-PC) as well as for two new polycarbonates having low molecular cross-sectional areas, namely a copolymer of tetraaryl polycarbonate and BPA-PC (TABPA-BPA-PC) and a triaryl polycarbonate homopolymer (TriBPA-PC). The glass transition temperatures of the new polymers are higher than the T g of BPA-PC (187 and 191 C vs. 148 C). Relative permittivity and loss measurements were carried out from 10 to 10 5 Hz over a wide temperature range, and results for the aand c-relaxation regions are discussed in detail. For the a-relaxation, the isochronal peak position, T a , scales approximately with T g . On the other hand, the peak temperature for the crelaxation is approximately constant, independent of T g . Also, in contrast to what is observed for a, c exhibits a strong increase in peak height as temperature/frequency increases and a significant difference is found between Arrhenius plots determined from isochronal and isothermal data analyses. Next, the c-relaxation region for comm-BPA-PC and associated activation parameters show strong history/purity effects. The activation parameters also depend on the method of data analysis. The results shed light on discrepancies that exist in the lit-erature for BPA-PC.

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Theoretical arguments linking monomer geometries to polymer fracture strengths and melt flow properties provide the rationale for design of a series of isomeric, high-aspect ratio bisphenols and new polycarbonates. An efficient synthesis of these monomers in addition to an optimal triphosgenation-based method for the synthesis of high molecular weight polycarbonates is presented. Preparation and polymerization of o-, meta-, and p-tetraaryl bisphenol A are reported, in addition to glass transition temperatures of the new polycarbonates. In accordance with expectations, the p- and m- isomers form ductile, amorphous high-heat films, while the o-isomer produces a relatively low-T g brittle glass.