Water Soluble Dual Responsive Star Copolymer for Encapsulation of Hydrophobic Dye Molecules

摘要

Synthesis of water soluble thermo and pH responsive 3-arm star shaped random copolymer of diethylene glycol methyl ether methacrylate (DEGMEM) and N, N diethylaminoethyl methacrylate (DEAEMA) is carried out by ATRP technique. The synthesized copolymer is characterized by ~1H NMR spectroscopy and gel permeation chromatography (GPC). The dual stimuli responsive behavior of the synthesized block copolymers is demonstrated using dynamic light scattering (DLS) and fluorescence spectroscopy. The copolymer is insoluble in water at pH 9.2 which is attributed to the hydrophobicity of -NEt_2 groups but at lower pH (pH 4 & 7) water solubility is observed due to protonation. Aggregation and dissociation behavior is only observed at pH 7 when the temperature is increased over 35 °C. Heating of the aqueous solution of the copolymer in presence of hydrophobic fluorescent molecule 'Nile red' over 35 °C shows a sharp increase in fluorescence intensity which again decreases with lowering of pH indicating temperature triggered encapsulation and pH triggered release of it. The increased hydrophobicity of -NEt_2 groups ensure aggregated structure at pH 7 over 35 °C. This is very much important in view of loading of hydrophobic molecules within the polymer scaffold in the pH range that remains in blood stream at physiological conditions.