Controlled grafting of polymer chains onto C60 and thermal stability of the obtained materials

‘Model’ polymer stars with a fullerene core and arms of defined molar masses and low polydispersities can be prepared by grafting ‘living’ anionic polymers or macro-radicals onto C 60 . The specific chemical reactivity of C 60 leads in both cases to a peculiar addition mechanism that allows to perfectly control the number of arms between 2 and 6. Upon addition of ‘living’ polymers, the carbanions generated on C 60 are delocalized on a single conjugated molecule, and the observed upper limit of six grafts results from this specific situation. It is also possible to take advantage of the increase of reactivity of the carbanionic sites located on the fullerene with their number to produce more sophisticated architectures such as ‘palm-trees’ or ‘dumbbells’. Upon heating (PS) x C 60 in solution the arms are released showing that the covalent bond between the fullerene and the polymer chains breaks first. The presence of this ‘weak’ bond is responsible for the decreased thermal stability of these compounds as compared to polystyrene. The reduced stability of any direct bond to C 60 seems general as the addition onto C 60 of only even number of macro-radicals generated through an atom transfer reaction results also from the lower stability of C 60 –Br as compared to PS–Br. The presence of grafted polymer chains on the C 60 allows organizing this fullerene at the nanoscale in a polymer matrix using the well known self-assembling of block copolymers. .