Synthesis of Sterically-Stabilized Latexes Using Well-Defined Poly(glycerol monomethacrylate) Macromonomers

Abstract

A range of well-defined methacrylic macromonomers based on glycerol monomethacrylate (GMA) has been synthesized by atom transfer radical polymerization (ATRP) in alcoholic media using an N-(dimethylamino)ethyl-2-bromoisobutyrylamide initiator. This tertiary amine-functionalized initiator was used to produce six homopolymer precursors with target degrees of polymerization of 20, 30, 40, 50, 60, and 70 via ATRP. These polymerizations proceeded to very high conversions (>95%) and afforded relatively low polydispersities (Mw/Mn ≤ 1.33). The tertiary amine end groups were then quaternized using 4-vinylbenzyl chloride (4-VBC) to afford the corresponding near-monodisperse styrene-functionalized PGMA macromonomers. These PGMA macromonomers were evaluated as reactive steric stabilizers for latex syntheses. Near-monodisperse submicrometer-sized and micrometer-sized polystyrene latexes were obtained by aqueous emulsion and alcoholic dispersion polymerization, respectively, as judged by scanning electron microscopy and dynamic light scattering studies. Attempted latex syntheses conducted in the absence of any macromonomer invariably resulted in macroscopic precipitation under dispersion polymerization conditions, with no evidence of latex formation. Higher molecular weight macromonomers (DP = 40 or 50) generally gave smaller, more monodisperse particles compared with the lower molecular weight macromonomers (DP = 20 or 30). Latex syntheses conducted in the presence of the PGMA50 homopolymer precursor produced particles with significantly larger diameters than those prepared with the corresponding styrene-functionalized PGMA50 macromonomer. Such control experiments confirmed the importance of having terminal styrene groups on the macromonomer chains for successful latex formation. FT-IR spectroscopy indicated the presence of the PGMA50 macromonomer within the polystyrene latex and XPS studies indicated that these stabilizer chains are located at (or very near) the latex surface, as expected. Finally, approximately micrometer-sized latexes can be produced by aqueous dispersion polymerization of 2-hydroxypropyl methacrylate in the presence of the PGMA50 macromonomer.