Synthesis of Aldehyde-Functionalized Fluorescent Micelles by Self-Assembly of a Hybrid Polymer Constructed by Hyperbranched Conjugated Polymer Core with Aldehyde End groups and Polyethylene Glycol Shell

Abstract

Water-dispersible fluorescent nano-/microspheres have been widely used as fluorescent probes in many fields. In this paper, aldehyde-functionalized fluorescent micelles are synthesized by self-assembly of end-modified hyperbranched poly(m-phenyleneethynylene-alter-p-phenyleneethynylene)(hb-PMPE). First, hb-PMPE with -Br end-groups(hb-PMPE-Br) is obtained by the polymerization of AB₂ monomer PhBr₂–C≡C–Ph–C≡CH, then the reaction of hb-PMPE-Br with 4-ethynylbenzaldehyde (EBA) gives end aldehyde-functionalized hyperbranched polymer hb-PMPE-CHO. Hence, hb-PMPE-CHO is reacted with aminooxy methoxypolyethylene glycol-2000 (NH₂O-MPEG2000) to link poly(ethylene glycol) (PEG) chains to the ends of hb-PMPE-CHO with partial residual aldehyde end-groups, resulting in aldehyde-functionalized amphiphilic polymer hb-PMPE-PEG. Fluorescent micelles with aldehyde-containing fluorescent hb-PMPE core and PEG shell are obtained by self-assembling hb-PMPE-PEG in water. The micelle diameter is determined by the PEG content in hb-PMPE-PEG, which can be controlled by the reaction weight ratio of NH₂O-MPEG2000/hb-PMPE-CHO. When the ratio of NH₂O-MPEG2000/hb-PMPE-CHO > 0.75/1, micelles with a diameter < 50 nm are obtained. The water dispersion of hb-PMPE-PEG-1/2 micelles (28.9 nm) emits bright green fluorescence with λ_max ≈ 490 nm under UV irradiation, and the emission intensity increases with increasing concentration.