Synthesis of β-cyclodextrin-based star polymers via a simplified electrochemically mediated ATRP

Cyclodextrin-based star polymers were synthesized using functionalized beta-cyclodextrin (beta-CD) core, and n-butyl acrylate (BA) as hydrophobic arms. The beta-CD core macroinitiator was prepared by the transesterification reaction of b-CD with 2-bromoisobutyryl bromide. The core-first method was chosen as the synthetic strategy as it allows good control over the polymer architecture. Star-shaped amphiphilic polymers were prepared via a simplified electrochemically mediated ATRP (seATRP) procedure under both potentiostatic and pseudo-galvanostatic conditions, utilizing only 50 ppm (40 ppm by weight (wt)) of Cu-II complex, much less than previously reported concentrations of catalyst of ca. 4,000-130,000 ppm (590-19,000 ppm (by wt)). The rate of the polymerizations (R-p) was controlled by applying different potentials E-app, with slower R-p observed using more positive E-app values thereby suppressing intermolecular termination reactions between growing arms, and subsequent starestar coupling. The polymerization results showed molecular weight evolution close to theoretical values while maintaining a narrow molecular weight distribution for the growing star polymer throughout the reaction. The differences between theoretical and measured MW originate in different hydrodynamic radii of stars and linear polymers used as standards for gel-permeation chromatography (GPC). Successful chain extension of the omega-functional arms with tert-butyl acrylate (tBA) resulted in star block copolymers and confirmed the living nature of the beta-CD-PBA star polymers prepared by seATRP. Moreover, the absence of radical coupling reactions during seATRP synthesis was confirmed by GPC analyses of the actual arm length of obtained star polymers and copolymers. (C) 2016 Elsevier Ltd. All rights reserved.