Controlled ring-opening (Co)polymerization of lactones initiated from cadmium sulfide nanoparticles

The coordination-insertion ring-opening polymerization (ROP) of ε-caprolactone (CL) was initiated from hydroxyl groups spread over the surface of cadmium sulfide nanoparticles with mean diameter in the range of 1.2nm. Such CdS nanoparticles were synthesized by reacting cadmium acetate and thiourea in the presence of thioglycerol as stabilizer. The core of the nanoparticles was composed of CdS while the OH-functionalized ligands were covalently and selectively bonded at the surface. The average number of hydroxyl groups available at the particle surface has been assessed by a modified Oilman's titration using n-butyllithium. The polymerization selectively occurred from the surface OH groups after activation into aluminum alkoxides species, which allows the polymerization of lactones from the surface. Solubilization of cadmium sulfide nanoparticles in organic solvent such as toluene or THF, i.e., both good solvents of PCL chains, attests for the covalent grafting of PCL chains onto the nanoparticle surface. Interestingly, the lactone polymerization was well controlled as evidenced by the sequential copolymerization of CL and δ-valerolactone (VL) for the surface grafting of P[CL-b-VL] diblock copolyesters onto the CdS nanoparticles.