PEGylation and polyPEGylation of nanodiamond

Polyethylene glycol (PEG) and poly(PEGMA) conjugated nanodiamond (ND) have been synthesized via “grafting to” and “grafting from” methods, respectively. In “grafting to” method, hydroxyl groups on ND surface were firstly oxidized to carboxyl groups, and then reacted with thionyl chloride to form acyl chloride groups. The acyl chloride functionalized ND (ND-COCl) was subsequently reacted with poly(ethylene glycol) monomethyl ether (mPEG) in the presence of triethylamine to generate mPEG conjugated ND (ND-mPEG). On the other hand, in “grafting from” method, ND-OH was modified with 2-bromoisobutyryl bromide (ND-Br), and then poly(PEG methyl ether methacrylate) (Poly(PEGMA)) chains were linked on the ND surface through surface-initiated atom transfer radical polymerization (ATRP) using ND-Br as the initiator and Cu(Br)/N,N,N′,N″,N″-pentmethyl diethylenetriamine (PMDETA) as the catalyst and ligand. The polymer conjugated ND particles were characterized using transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). TGA analyses demonstrated that the polymer weight ratios through “grafting to” and “grafting from” methods were 29.8% and 34.4%, respectively. The mPEG and poly(PEGMA) conjugated ND nanoparticles exhibited enhanced dispersibility in organic media. More importantly, due to the relative high graft ratios and molecular weight, poly(PEGMA) functionalized ND was also dispersed well in water. Given the excellent physicochemical and biological properties of PEG and ND, the methods described in current work might be useful for the preparation of functional ND nanoparticles for potential biomedical applications.