Influence of plasticizer configurational changes on the dielectric characteristics of highly plasticized poly(vinyl chloride)

Three citrate-related compounds [Citroflex A-4 (CFA4), Citroflex A-6 (CFA6), and Citroflex B-6 (CFB6)] and six sebacate-related compounds [dimethyl sebacate (DMS), diethyl sebacate (DES), dibutyl sebacate (DBS), dioctyl sebacate (DOS), dioctylazelate (DOZ), and dioctyl adipate (DOA)] were used to evaluate the effects of configurational changes in plasticizer on the dielectric properties of ion-selective poly(vinyl chloride) membranes. Tridodecylamine (TDDA) and potassium tetrakis-4-chlorophenyl borate (KTpClPB) were used as neutral charge carriers and negative sites, respectively. Using parallel plate sensors, the dielectric properties [ionic conductivity (sigma) and tan delta] of the plasticized PVC membranes were determined at temperatures from -100 to + 100 degrees C and seven log frequencies ( -1, 0, 1, 2, 3, 4, and 5 Hz). Generally, increasing the amount of plasticizer in the membrane improved the sigma and lowered the temperature of the tan delta peak. A positive linear correlation existed between the log sigma and the log phr ratio for a given temperature and frequency, when no data was included for membranes below the melting temperature of the plasticizer. When plotted versus temperature, the slopes of all these lines passed through a maximum between 0 and 60 degrees C. The intercepts of all these lines increased monotonically with increasing temperature. These intercepts were highly dependent on the frequency at low temperatures, becoming less frequency dependent as the temperature increased. Having established that configurational changes of the plasticizers had no effect above the melting point of each plasticizer, global nomograms were only required for the citrate-and sebacate-related plasticizers, respectively. Using the appropriate nomogram for a selected plasticizer, the sigma could be predicted at a given phr ratio, temperature, and frequency. (C) 1998 Elsevier Science Ltd. All rights reserved.