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 (iBu3Al) 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 iBu3Al allows the formation of polymers with high end-group fidelity (azide groups at the α-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.

Dielectric relaxation is used to verify the bidirectional growth of arms in poly(glycidyl phenyl ether) (PGPE) synthesized by ring-opening polymerization with ethylene glycol and a phosphazene base, t-BuP 4 , in the presence and absence of triisobutylaluminum (i-Bu 3 Al). The dielectric relaxation is highly sensitive to changes in the dipolar moment orientation along the chain contour, allowing us to precisely identify whether the polymer is composed by "one arm" or "two arms" as well as to verify the arm symmetry. By means of broadband dielectric spectroscopy (BDS), we evaluated the dipolar microstructure of synthesized polymers and observed that in the absence of i-Bu 3 Al the polymers are certainly composed by two symmetric arms, whereas those obtained in the presence of i-Bu 3 Al are contaminated with large amounts of "one-arm" byproducts, in agreement with the data obtained by MALDI-ToF MS. Furthermore, BDS allowed us to quantify the relative amounts of one-arm impurities in two-arm PGPE samples, an analysis that cannot be performed by either MALDI-ToF MS or NMR.

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