The Synthesis and Evaluation of Friedel-Crafts Polymers

Abstract

The application of the Friedel-Crafts reaction to the production of polymers having novel and useful properties has been studied. Particular attention has been paid to the potential use of such materials in high temperature electrical insulation applications. Several resin systems have been examined and an attempt has been made to correlate the initial structure of the reactants and their reactivity with the properties of the resins produced. p-Xylylene glycol dimethyl ether (p-XGDME) was used as the reactive monomer in the bulk of the work. Terphenyl and diphenyl oxide (DPO) were chosen as substrate monomers because of their comparatively large size in the hope that they would yield polymers with well spaced cross-links which would be flexible enough for insulation applications. In the case of phenyl this was not achieved but with DPO a resin was produced which had attractive handling characteristics and could be used as an impregnating resin for the windings of high temperature electrical machines. Mouldings and laminates of good electrical properties were also produced but the interlaminar bonding in glass cloth laminates was rather poor. Different solvents were shown to have very marked effects on the rate of the DPO/p-XGDME reaction and also on the properties of the resins produced. One resin was found to give much improved glass/resin bonding than was achieved with the bulk prepared DPO/p-XGDME resins. The curing mechanisms of a terphenyl and a DPO resin were examined by infra red spectroscopy and by weight loss, and in both cases loss of unreacted monomer occurred during cure. Further condensation took place yielding additional cross-links; and simultaneously oxidation of methylene bridges to carbonyls, and methoxymethyl groups to carboxylic acid groups occurred. The deactivated molecule, 4, 4'di(chloromethyl) benzophenone, was substituted for p-XGDNE in an attempt to limit branching in the polymer but its reactions were very slow and the products no more linear. The literature discrepancy about the melting point of 4,4' di(chloromethyl) benzophenone was resolved in favour of 103°C.