Well-Defined Amphiphilic C60-PEG Conjugates: Water-Soluble and Thermoresponsive Materials

For the preparation of well-defined H2O-soluble C-60 polymers, several C-60-PEG conjugates were prepared from a C-60 biscarboxylic acid derivative and monodisperse NH2-PEGs (NH2-EG(n), n=4-36) via amide conjugation. When the relatively long PEGs (EG(n), n12) were employed, the C-60-PEG conjugates became completely H2O-soluble by forming micelle-like structure shown by the data of surface tension, DLS, and cryo-TEM. Interestingly, these H2O-soluble C-60-PEG conjugates (C-60(EG(n))(2), n=12-36) showed reversible thermoresponse to form larger aggregates (ca. 1m by DLS) at higher temperatures. The temperature for the aggregation was related to the lengths of PEGs attached to C-60; 29 degrees C (C-60(EG(n))(2), n=12), 51 degrees C (n=20), and 72 degrees C (n=36). This thermoresponse was speculated to occur by dehydration of well-organized PEG chains in the micelle-type structure of monodisperse C-60-PEG caused by gauche-to-anti conformational change of PEG anchors. This thermoresponse of well-defined amphiphilic C-60-PEG conjugates indicates potential applications in areas such as temperature sensors and thermoresponsive materials.