Near-Monodisperse Poly(2-(methacryloyloxy)ethyl phosphorylcholine)-Based Macromonomers Prepared by Atom Transfer Radical Polymerization and Thiol−Ene Click Chemistry: Novel Reactive Steric Stabilizers for Aqueous Emulsion Polymerization

摘要

Poly(2-(methacryloyloxy)ethyl phosphorylcholine)n(PMPC) macromonomers have been prepared by thenatom transfer radical polymerization (ATRP) of 2-n(methacryloyloxy)ethyl phosphorylcholine (MPC) using anbifunctional disulfide-based initiator. To attach a terminalnpolymerizable methacrylate group, the central disulfide bondnwas cleaved and the resulting thiols were conjugated to 3-n(acryloyloxy)-2-hydroxypropyl methacrylate using tris(2-ncarboxyethyl)phosphine (TCEP) in water. Here TCEP servesnas both the disulfide cleavage agent and also the catalyst for thensubsequent Michael addition, which is highly selective for the acrylate group. The resulting methacrylate-terminatednmacromonomers were used as a reactive steric stabilizer for the aqueous emulsion polymerization of styrene, yielding nearmonodispersenPMPC-stabilized polystyrene (PS) latexes of around 100−200 nm in diameter. As a comparison, the disulfidecontainingnPMPC homopolymer precursor and the intermediate thiol-functional PMPC homopolymer (PMPC−SH) were alsonevaluated as potential steric stabilizers. Interestingly, near-monodisperse latexes were also obtained in each case. These threensterically-stabilized latexes, prepared using either PMPC macromonomer, disulfide-based PMPC homopolymer, or PMPC−SHnhomopolymer as a reactive steric stabilizer, remained colloidally stable after both freeze−thaw experiments and the addition of annelectrolyte, indicating that a coronal layer of PMPC chains prevented flocculation in each case. In contrast, both a chargestabilizednPS latex prepared in the absence of any steric stabilizer and a PS latex prepared in the presence of a nonfunctionalnPMPC homopolymer exhibited very poor colloidal stability when subjected to a freeze−thaw cycle or the addition of annelectrolyte, as expected.