PEGylated Functional Nanoparticles from a Reactive Homopolymer Scaffold Modified by Thiol Addition Chemistry

Well-defined reactive polymer scaffolds are useful building blocks for a variety of biomedicine and nanotechnology applications. In this study, we have converted a RAFT-synthesized thiol-functional homopolymer scaffold (poly(pyridyl disulfide ethyl methacrylate), PPDSM) to poly(ethylene glycol) conjugated (PEGylated) nanoparticles via a straightforward approach. Poly(ethylene glycol) (PEG) was grafted to the reduced PPDSM via radical-mediated thiol-ene or Michael additions. The yield of PEG grafting via radical-mediated thiol-ene reaction and Michael addition was 68 +/- 2 and 73 +/- 1 mol %, respectively, of the total functional groups on the scaffold, as determined by H-1 NMR spectroscopy. The grafting yield via Michael addition reactions was non-linearly proportional to the reducing agent concentration used (thus the number of free thiols created on the polymer chain). It was observed by UV-vis spectroscopy that PEG grafting via Michael addition to the PPDSM takes place simultaneously with inter- and intrachain thiol disulfide exchange reactions. Dynamic light scattering (DES) measurements of PEG-acrylate (M-n = 2000 g/mol) grafted PPDSM (74 mol % grafting yield) in water showed the presence of particles with an average hydrodynamic diameter of 99 +/- 8 nm and polydispersity index (PDI) of 0.22 +/- 0.02. Atomic force microscopy (A FM) analysis of the same sample revealed the presence of spherical shape particles. H-1 NMR analysis of the same PEG grafted PPDSM nanoparticles in different solvents revealed that the PPDSM backbone in water was surrounded by PEG chains. Overall, the results indicate that simply grafting PEG to PPDSM homopolymer scaffold can be a straightforward route to the generation of nanoparticles with a biocompatible, stealth shell, and the present synthetic approach can be exploited further for the generation of PEGylated functional nanoparticles for potential drug delivery applications.