We evaluate the use of tetrabutylammonium azide (N3NBu4) as an anionic ring-opening polymerization initiator for synthesizing azide-terminated linear poly(glycidyl phenyl ether) and then generating monocyclic structures with high purity. In particular, we perform a detailed study on the end-group fidelity of polymers obtained by initiation with N3NBu4 in the presence and absence of trisisobutylaluminum (iBu(3)Al) and evaluate the purity of the cyclic structures obtained via copper-catalyzed alkyne-azide cycloaddition "click" reaction. We demonstrate that in contrast to the polymerization initiated by N3NBu4 alone, the polymerization performed in the presence of iBu(3)Al allows the formation of polymers with high end-group fidelity (azide groups at the a position) for M-n < 20 kDa. The cyclic purity is evaluated by SEC with triple detection and dielectric spectroscopy. The latter technique, although not conventional for such a purpose, is shown to be very convenient to ensure cyclic purity in polymers showing an end-to-end dielectric relaxation mode.