Synthesis and Characterization of Biocompatible Sulfoxide-Containing Molecular Bottlebrushes

Macromolecular bottlebrushes (MBs) are emerging as an attractive polymer architecture for biomedical applications. Herein, synthesis and characterization of sulfoxide-containing water-soluble MBs with poly(2-(methylsulfinyl)ethyl acrylate) (PMSEA) side chains with varying grafting densities are reported. Highly hydrophilic PMSEA side chains were prepared by grafting-from poly(2-bromoisobutyryloxyethyl methacrylate) (PBiBEM) using photoATRP with either CuBr2/TPMA (tris(2-pyridylmethyl)amine), CuBr2/TPMA*3 (tris([(4-methoxy-2,5-dimethyl)-2-pyridyl]methyl)amine), or CuBr2/Me6TREN (tris(2-dimethylaminoethyl)amine), which were photochemically reduced to the appropriate amount of activators CuBr/ligand to start atom transfer radical polymerization (ATRP). Kinetic experiments showed that the polymerization was the fastest using CuBr2/Me6TREN at 6-fold excess of ligand to Cu. Additionally, the increase of ligand concentration resulted in a faster reaction with CuBr2/Me6TREN. A series of PMSEA MBs with grafting densities of 30%, 50%, and 100% was synthesized. The PMSEA MBs exhibited tunable hydrodynamic lubrication properties and low cytotoxicity against different types of cells. PMSEA MBs reveal rheological properties characteristic for nonentangled polymer melts. Densely grafted PMSEA MBs showed a nonlinear relationship between the coefficient of friction and the applied force.