Depolarization current of a novolac p‐fluorophenol‐formaldehyde resin

Abstract

A Novolac p‐fluorophenol‐formaldehyde (NFF) resin was prepared by condensation of p‐fluorophenol with formaldehyde. DSC showed the glass transition effect or coinciding endothermal peak depending upon the thermal history of samples. It is supposed that the peaks are caused by breaking of the intermolecular bondings in the resin during the glass transition. The bondings are formed in the resin during the storage at room temperature. Thermally stimulated depolarization current (TSDC) measurements were carried out in the temperature range of 290 to 350 K, with the samples having an average number molecular weight M̄n of 375 and 434. TSDC curves mainly showed the dipolar relaxation α peaks. The influence of poling temperatures, the influence of M̄n, the activation energy Ea, and the physical ageing of the samples were investigated. Physical ageing was determined as the reciprocal polarizability Rp vs. time of ageing. Samples. with higher M̄n showed a higher glass transition temperature, a lower Ea, and a higher increase in Rp than the sample with lower M̄n. The increase in M̄n increased the rigidness of NFF samples. The effects are attributed to the strong hydrogen bonding. The comparison with analogous results in novolac phenol‐formaldehyde resin without fluorine is given.

Thermally stimulated depolarization current of novolac resin

“…2. Such an increase in the peaks for a system with lower Mn was also observed for fluorinated NPF resin [11]. Curve B is related to the primary batch of resin, curve A to the low molecular fraction, and curve C to the high molecular residue.…”