Synthesis, characterization and association behavior of linear-dendritic amphiphilic diblock copolymers based on poly(ethylene oxide) and a dendron derived from 2,2′-bis(hydroxymethyl)propionic acid

Abstract

Two new amphiphilic linear-dendritic block copolymers (LDBCs) composed of poly(ethylene oxide) (PEO) and a dendron derived from 2,2′-bis(hydroxymethyl)propionic acid (bis-MPA), PEO(5k)-b-G3-(C₁₈H₃₅O₂)₈ and PEO(5k)-b-G3-(C₂H₃O₂)₈ were synthesized by click chemistry. The structures of the LDBCs were determined by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography (GPC). Furthermore, their aggregation behaviors at 298.15 K for these two synthesized polymers were studied by fluorescence spectroscopy and isothermal titration calorimetry (ITC). The fluorescence measurements indicate that both of the synthesized polymers have evident aggregation behavior in aqueous solution due to the significant hydrophobic interactions between the branched groups. Thus we characterized the thermodynamics of their aggregation by ITC and obtained their critical micelle concentrations (CMC), as well as the positive enthalpy of micellization for (PEO(5k)-b-G3-(C₁₈H₃₅O₂)₈), which suggests that its molecular self-assembly process is entropy-driven. Furthermore, the micellar morphologies of the copolymers in aqueous solution were verified by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The spherical polymeric micelles of PEO(5k)-b-G3-(C₁₈H₃₅O₂)₈ and PEO(5k)-b-G3-(C₂H₃O₂)₈ were observed and their diameters are 70 nm and 160 nm, respectively. The length of the alkyl chain of the periphery carboxylic acid affects their CMCs and the size of micelles. Finally, the biocompatibility of both LDBCs was evaluated, and they were found to have relatively low cytotoxicity, which provides potential opportunities for a variety of biomedical applications.