Preparation of Biocompatible Sterically Stabilized Latexes Using Well-Defined Poly(2-(methacryloyloxy)ethyl phosphorylcholine) Macromonomers

Abstract

A range of well-defined methacrylic macromonomers based on the biomimetic monomer 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) were synthesized by atom-transfer radical polymerization (ATRP) in alcoholic media using 2-(dimethylamino)ethyl-2-bromoisobutyrylamide. This tertiary amine-functionalized initiator was used to produce homopolymer precursors of various chain lengths via ATRP. These polymerizations were relatively well controlled (M(w)/M(n) < or = 1.30), provided that the target degree of polymerization (DP) did not exceed 30. For higher target DPs, polymerization was only poorly controlled and characterized by broad molecular weight distributions (M(w)/M(n) = 1.50-2.31). The tertiary amine end-group of each nearly monodisperse homopolymer precursor was then quaternized using 4-vinylbenzyl chloride (4-VBC) to afford the corresponding styrene-functionalized macromonomers. PMPC(30) macromonomer proved to be an effective reactive steric stabilizer for the formation of polystyrene latexes when employed at 10 w/w % on the basis of the styrene monomer. Nearly monodisperse submicrometer-sized and micrometer-sized latexes were prepared by aqueous emulsion and alcoholic dispersion polymerization, respectively, as judged by scanning electron microscopy and dynamic light scattering studies. In contrast, attempted alcoholic dispersion polymerization conducted either in the presence of the PMPC(30) homopolymer precursor or in the absence of any macromonomer always resulted in macroscopic precipitation. Such control experiments confirmed the importance of the terminal styrene groups on the macromonomer chains for successful latex formation. FTIR spectroscopy indicated the presence of the PMPC(30) macromonomer within the polystyrene latex, and XPS studies indicated that these stabilizer chains are located at (or very near) the latex surface, as expected. Using PMPC(20) and PMPC(10) macromonomers for the alcoholic dispersion polymerization of styrene led to latexes with substantially broader size distributions compared to those produced using the PMPC(30) macromonomer under the same conditions. Finally, these new sterically stabilized latexes exhibit excellent freeze-thaw stability and salt tolerance.