Solvent-free chemical modification of fullerence C60 by anamino-terminated polyethylene glycol

Abstract

The solvent-free chemical modification (SFM) of fullerene (C60) by polyethylene glycol with amino terminal (amino-PEG) was studied in order to improve the fullerene dispersability. The effect of the stirring rate and the C60 particle size on the modification yield was investigated in the temperature range 60-120°C for 3-24 h. As a result, 65 % of C60 was modified at 60°C for 24 hr to disperse in ethanol. The effect of C60 particle size on the yield was found to be more significant than that of the stirring rate. Therefore, the SFM is more sensitive to the collision frequency between C60 and amino-PEG compared to the diffusion of C60 in amino-PEG.In order to understand the chemical modification mechanism, simulation was performed based on a shrinking-core model assuming a chemical reaction as a rate limiting step.Using this model it was possible to estimate the number of amino-PEG molecules attached to C60. The results of simulation fit well the gel permeation chromatography (GPC) data collected in the early period of reaction considering that one amino-PEG attached to C60. As for the final period of reaction, the number of attached amino-PEG molecules increases according to the GPC data but the simulation shows opposite tendency.This tendency was explained by decrease in C60 surface activity and by the additional reaction between products in the fluid phase.