Clickable Stars by Combination of AROP and Aqueous AGET ATRP

A series of star-shaped poly(ethylene oxide) (PEO) with azide groups at the end of each arm were synthesized by combination of anionic ring-opening polymerization (AROP) and aqueous activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP). First, α-azido, ω-hydroxy heterofunctional PEOs were prepared by AROP of ethylene oxide (EO) using tetrabutylammonium azide as initiator and triisobutylaluminum as catalyst. Then, a clickable PEO ATRP macroinitiator, α-azido, ω-bromoisobutyryl heterofunctional PEO, was synthesized by an esterification of the ω-hydroxy end group with 2-bromoisobutyryl bromide. Finally, an AGET ATRP of ethylene glycol diacrylate (EGDA) was carried out in water using the α-azido, ω-bromoisobutyryl heterofunctional PEOs as macroinitiator and surfactant. The absolute molecular weights of the products were characterized by static laser light scattering in water. Azide PEO stars with M w = 6.58 × 106 and average 309 arms were obtained using azide PEO macroinitiators with M n = 9800 and [EGDA]/[MI] = 58. However, control over topology was lost for [EGDA]/[MI] > 100, resulting in irregular aggregates. The core−shell morphology of the functional star PEOs was observed by transmission electron microscopy. Fluorescent PEO stars were obtained by “clicking” dansyl probes onto the star shell, as verified by fluorescence spectra.