Dielectric relaxations in poly(glycidyl phenyl ether): Effects of microstructure and cyclic topology

Abstract

Cyclic and linear, isoregic and aregic, and isotactic and atactic poly(glycidyl phenyl ether) (PGPE) with molecular weights up to Mw = 5.5 kg/mol are synthesized by ring-opening polymerization of glycidyl phenyl ether. Initiation with tetrabutylammonium fluoride leads to isoregic linear polymers with ∼95% regular linkages, and initiation with B(C6F5)3 and B(C6F5)3/water leads to aregic cyclic and linear polymers, respectively, with ∼50% regular linkages as quantified by 13C NMR. Local, segmental, and chain dynamics in PGPE is investigated by broadband dielectric spectroscopy (10–2–106 Hz). The β-relaxation for linear PGPE is separated into two contributions arising from the motions of side groups and end groups with activation energies of 35.4 and 23.8 kJ/mol, respectively. The β-relaxation process for cyclic PGPE shows the same activation energy as that shown by the side-group contribution in linear PGPE, indicating that topology does not play a key role on the side-group local dynamics. Moreover, cyclic PGPE samples show higher calorimetric and dynamic glass transition temperatures as well as lower dynamic fragility compared to linear chains. Unexpectedly from topological considerations, cyclic PGPE shows low frequency dielectric contributions that can be attributed to short wavelength internal ring motions and that are detectable by dielectric relaxation due to the aregic nature of the rings.