Summary: Poly(vinyl acetate) chains end‐capped by a Co(acac)2 complex [PVAc‐Co(acac)2] were prepared by bulk cobalt‐mediated radical polymerization (CMRP) of vinyl acetate and used for grafting fullerene (C60) with four PVAc arms at low temperature (30 °C). A photoactive water‐soluble poly(vinyl alcohol)/C60 nanohybrid was then prepared by hydrolysis of the PVAc arms of the nanohybrid. Because of photoactivity and very low cytotoxicity, this type of water‐soluble nanohybrid is very promising for the photodynamic cancer therapy.

Star-shaped poly(ε-caprolactone) (PCL) with a fullerene (C60) core, C60[N(CH2)12OPCLOH] x , was successfully synthesized by reaction of azide-terminated PCL with C60. Both the experimental conditions and the stoichiometry were optimized, such that an average of six PCL chains was grafted per fullerene core. The molecular weight of the polyester chains directly controlled the length of the arms of the star-shaped polymers. Singlet oxygen was generated on irradiation of the C60[N(CH2)12OPCLOH] x nanohybrids. These C60[N(CH2)12OPCLOH] x nanohybrids were then processed in two kinds of nanomaterials. First, they were encapsulated within the core of micelles formed by biocompatible amphiphilic block copolymers. In water, the particle size distribution of these nanoparticles was narrow, and their diameter was in the range of 100 to 200 nm. Second, C60-containing micro-/nanosized polymer fibers were prepared, for the first time, by electrospinning. The average diameter of the fibers was varied by tuning the PCL/C60[N(CH2)12OPCLOH] x weight ratio. Grafting of polyester chains onto C60 is thus a suitable strategy for producing easily processable C60 and attractive building blocks for incorporation of C60 in nanomaterials.

Well-defined poly(vinyl acetate) (PVAc) and poly(N-vinylpyrrolidone)-co-poly(vinyl acetate) (PNVP-co-PVAc) chains end-capped by Co(acac)(2) (acac=acetylacetonate) and prepared by cobalt-mediated radical polymerization (CMRP) are grafted onto a fullerene. Homolytic Co-C bond cleavage of the polymer chain ends at 30 degrees C releases the polymeric radicals that add onto C(60), thereby leading to the corresponding PVAc/C(60) and PNVP-co-PVAc/C(60) nanohybrids. The [polymer-Co(acac)(2)]/[C(60)] molar ratio was varied to adjust the structure of the nanohybrids, and more particularly the number of grafted arms. Finally, the potential of the hydrosoluble PVOH/C(60) nanohybrids, which result from the methanolysis of the ester groups of PVAc/C(60), and of the PNVP-co-PVAc/C(60) nanohybrids as photosensitizers for photodynamic therapy (PDT), was approached. First, photobleaching tests demonstrated the ability of these nanohybrids to produce singlet oxygen upon irradiation, which can play a role in cell damage. Second, cell viability assays demonstrated that both types of nanohybrids are deprived of intrinsic cytotoxicity in the dark, whereas they promoted significant cell mortality when subjected to light treatment. The selective response of these materials to irradiation makes them promising compounds for PDT.