Synthesis of biopolymer-grafted nanodiamond by ring-opening polymerization

• We report an efficient method for covalently linking the biopolymer to ND.
• Biopolymer-grafted ND is prepared by surface initiated ring-opening polymerization.
• Biopolymer-grafted ND shows a superior dispersion in organic solvents.
• It may promise multipurpose applications in biomedical systems.

We have developed an efficient and biological method for the covalent functionalization of nanodiamond (ND) biopolymers. ND-grafted-poly(l-lactic acid) (ND-g-PLLA) and ND-grafted-poly(ε-caprolactone) (ND-g-PCL) were prepared by surface-initiated ring-opening polymerization. After homogenization of the surface by mixed acids and thionyl chlorides, the surface of ND was modified with 1,6-hexanediol to possess hydroxyl groups, which could be used as coinitiators to polymerize l-lactide or ε-caprolactone to yield ND grafted with bio-polyesters. The FT-IR, Raman and NMR spectra revealed that the polyester chains were covalently attached to the ND and the weight gains as a result of the functionalized ND particles were determined by TGA analysis. The ND-g-PLLA and ND-g-PCL were both well dispersed in the organic solvents and the average diameters were measured. The TEM images demonstrate that the dispersion of pristine ND has been significantly improved after modification of ND with PLLA or PCL.