Cyclodextrin-overhanging hyperbranched core-double-shell miktoarm architectures: Synthesis and gradient stimuli-responsive properties

We report the synthesis and gradient stimuli-responsive properties of cyclodextrin-overhanging hyperbranched core-double-shell miktoarm architectures. A ionic hyperbranched poly(β-cyclodextrin) (β-CD) core was firstly synthesized via a convenient "A ₂+B ₃" approach. Double-layered shell architectures, composed of poly(N-isopropyl acrylamide) (PNIPAm) and poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) miktoarms as the outermost shell linked to poly(N,N-diethylaminoethyl methacrylate) (PDEAEMA) homoarms which form the inner shell, were obtained by a sequential atom transfer radical polymerization (ATRP) and parallel click chemistry from the modified hyperbranched poly(β-CD) macroinitiator. The combined characterization by ¹H NMR, ¹³C NMR, ¹H- ²⁹Si heteronuclear multiple-bond correlation (HMBC), FTIR and size exclusion chromatography/multiangle laser light scattering (SEC/MALLS) confirms the remarkable hyperbranched poly(β-CD) core and double-shell miktoarm architectures. The gradient triple-stimuli-responsive properties of hyperbranched core-double-shell miktoarm architectures and the corresponding mechanisms were investigated by UV-vis spectrophotometer and dynamic light scattering (DLS). Results show that this polymer possesses three-stage phase transition behaviors. The first-stage phase transition comes from the deprotonation of PDEAEMA segments at pH 9-10 aqueous solution under room temperature. The confined coil-globule conformation transition of PNIPAm and PDMAEMA arms gives rise to the second-stage hysteretic cophase transition between 38 and 44 °C at pH 10. The third-stage phase transition occurs above 44 °C at pH = 10 attributed to the confined secondary conformation transition of partial PDMAEMA segments. This cyclodextrin-overhanging hyperbranched core-double-shell miktoarm architectures are expected to solve the problems of inadequate functionalities from core layer and lacking multiresponsiveness for shell layers existing in the dendritic core-multishell architectures.