Stimuli-responsive and micellar behaviors of star-shaped poly[2-(dimethylamino)ethyl methacrylate]-b-poly[2-(2-methoxyethoxy)ethyl methacrylate] with a β-cyclodextrin core

Abstract

A series of star-shaped block copolymers (CDPDPM) of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) with tunable stimuli-responsive behavior are synthesized via sequential atom transfer radical polymerization (ATRP) with the 2-bromoisobutyryl-terminated β-cyclodextrin (β-CD) as a core. The properties of these star-shaped copolymers are characterized by FT-IR, NMR and GPC analyses. Meanwhile, the thermo-sensitive behaviors of CDPDPM with different compositions and pH values are investigated by dynamic light scattering (DLS) and UV–vis measurements. The results have shown that the synthesized polymer CDPDPM exhibits both pH- and thermo-responsive behaviors in aqueous solutions. The star-shaped copolymers with the nearly equal mole fraction of DMAEMA and MEO2MA show two-step thermo-induced aggregation behavior in water at a pH near the isoelectric point (IEP), which corresponds to the formation of branch aggregates and large aggregates consisting of clustered branch aggregates, respectively. The mole fraction of DMAEMA and MEO2MA in polymer affects the thermal-responsive behaviors of polymer itself. Moreover, the micellar behaviors of the synthesized copolymers in aqueous solution are explored. The aggregation process of the copolymer can be generalized into intramolecular aggregation of the hydrophobic chains (corresponding to CI), formation of premicelles, the aggregation and rearrangement of the premicelles (namely CMC), as well as the formation of multicore structures. The CI and CMC values depend on both the MEO2MA molar fraction and the carbon backbone length of polymers. The aggregation number (N) and the sizes of polymer micelles (Dh) vary with the polymer composition, polymer concentration and ambient environment.