A pH-sensitive double [60]fullerene-end-capped polymers via ATRP: Synthesis and aggregation behavior

A double [60]fullerene (C60)-end-capped water-soluble polymer [C60-DMAEMA68-C(CH3)2COOCH2]2 was synthesized by cycloaddition of the double azido-terminated [DMAEMA68-C(CH3)2COOCH2]2 with C60. The well-defined [Br(Cl)-DMAEMA68-C(CH3)2COOCH2]2 was first synthesized via ATRP using ethylene bis(2-bromoisobutyrate) as initiator in ethanol. TGA and spectrophotometric analyses confirmed that monoaddition to C60 had occurred. In aqueous solution, [C60-DMAEMA68-C(CH3)2COOCH2]2 self-assembled into flower micelles. The aggregation behaviors in unbuffered distilled water and in acidic solution at pH 3 were studied by laser light scattering (LLS). The micelles formed in distilled water has an aggregation number (Nagg) of ∼242 which is about three times larger than that at pH 3 solution (Nagg = 81). However, the micellar size is bigger at pH 3, due to the highly stretched corona resulting from the charge repulsion among the protonated amino groups. After calcination, the C60 core could be seen clearly by AFM. The critical micelle concentration (CMC) of [C60-DMAEMA68-C(CH3)2COOCH2]2 is lower in unbuffered distilled water (28.6 mg dm−3) than in solution at pH 3 (176.8 mg dm−3).