Electron beam crosslinking of fluoroalkoxy, methoxyethoxyethoxy, and substituted phenoxy polyphosphazenes: Physical and chemical characterization andcomparison to a thermally induced free radical process and ionic complexation

Electron beam, thermal free radical, and cationic complexation mechanisms h ave been employed to investigate crosslinking in selected polyphosphazenes. In polyphosphazenes functionalized with o-allylphenol to facilitate free r adical crosslinking, maximum crosslink density was achieved after 10 min at 130 degrees C utilizing benzoyl peroxide as an initiator. Electron beam ra diation was found to give an increased crosslink density with increased dos e. The dose-crosslink density relationship observed for a aryloxyphosphazen e terpolymer PPXP also was seen in poly[bis(2,2'-(methoxyethoxy)ethoxy)phos phazene] (MEEP). However, with two lots of a fluoroalkoxyphosphazene an ini tial crosslink density was achieved at a lower electron beam exposure with no additional crosslink density observed with increasing dose. These measur ements are observations of net crosslinking, which is the result of crossli nking processes balanced by chain scission processes. DSC revealed that nei ther thermal- nor electron beam-initiated crosslinking cause any significan t change in the T-g, of the polymer. Metal ion complexation with MEEP consi stently gave T-g values that were higher than MEEP. The T-g values measured for both MEEP and the lithium-complexed MEEP were unaffected by electron b eam irradiation. These data suggest the location of lithium complexation ma y be at the nitrogen lone electron pair on the backbone, representing a new mechanism of lithium complexation in phosphazenes. (C) 2000 John Wiley & S ons, Inc.